v3.26.1
Fair value measurements - Schedule of quantitative and qualitative information regarding significant unobservable inputs (Detail) - Recurring [Member] - Level 3 [Member]
¥ in Billions
 12 Months Ended
Mar. 31, 2026
JPY (¥)
Mar. 31, 2025
JPY (¥)
Mar. 31, 2024
JPY (¥)
Quantitative information about significant unobservable inputs [Line Items]      
Fair Value, Financial Instrument, Assets ¥ 1,290 ¥ 1,330 ¥ 1,041
Fair Value, Financial Instrument, Liabilities 575 593 557
Trading assets and private equity and debt investments [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Fair Value, Financial Instrument, Assets 403 621 470
Trading assets and private equity and debt investments [Member] | Equities [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Fair Value, Financial Instrument, Assets ¥ 14 ¥ 21 8
Trading assets and private equity and debt investments [Member] | Equities [Member] | DCF / Option models [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Interrelationships between valuation inputs [1] Not applicable Not applicable  
Trading assets and private equity and debt investments [Member] | Equities [Member] | DCF / Option models [Member] | Credit spreads [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 0.029 0.025  
Impact of increases in significant unobservable valuation inputs [3],[4] Lower fair value Lower fair value  
Trading assets and private equity and debt investments [Member] | Equities [Member] | DCF / Option models [Member] | Credit spreads [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [5],[6] 0.029 0.025  
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Fair Value, Financial Instrument, Assets ¥ 146 ¥ 103 80
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | DCF [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Interrelationships between valuation inputs [1] No predictable interrelationship No predictable interrelationship  
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | DCF [Member] | WACC [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Lower fair value Lower fair value  
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | DCF [Member] | WACC [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 0.075 0.058  
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | DCF [Member] | WACC [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 0.162 0.173  
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | DCF [Member] | WACC [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [5],[6] 0.122 0.116  
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | DCF [Member] | Growth rates [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Higher fair value Higher fair value  
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | DCF [Member] | Growth rates [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 0 0  
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | DCF [Member] | Growth rates [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 0.02 0.02  
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | DCF [Member] | Growth rates [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [5],[6] 0.017 0.012  
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | DCF [Member] | Credit spreads [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Lower fair value Lower fair value  
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | DCF [Member] | Credit spreads [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 0 0.079  
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | DCF [Member] | Credit spreads [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 0.499 0.11  
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | DCF [Member] | Credit spreads [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [5],[6] 0.085 0.094  
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | DCF [Member] | Liquidity discounts [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Lower fair value Lower fair value  
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | DCF [Member] | Liquidity discounts [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 0 0.05  
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | DCF [Member] | Liquidity discounts [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 0.30 0.30  
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | DCF [Member] | Liquidity discounts [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [5],[6] 0.11 0.16  
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | Market multiples [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Interrelationships between valuation inputs [1] No predictable interrelationship No predictable interrelationship  
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | Market multiples [Member] | EV/EBITDA ratios [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Higher fair value Higher fair value  
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | Market multiples [Member] | EV/EBITDA ratios [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 5.9 7.8  
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | Market multiples [Member] | EV/EBITDA ratios [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 11.4 16.2  
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | Market multiples [Member] | EV/EBITDA ratios [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [5],[6] 8.9 10  
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | Market multiples [Member] | PE Ratios [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Higher fair value Higher fair value  
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | Market multiples [Member] | PE Ratios [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 12.1 10.6  
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | Market multiples [Member] | PE Ratios [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 20.8 28.4  
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | Market multiples [Member] | PE Ratios [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [5],[6] 15.2 15.2  
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | Market multiples [Member] | Liquidity discounts [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Lower fair value Lower fair value  
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | Market multiples [Member] | Liquidity discounts [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 0.10 0.05  
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | Market multiples [Member] | Liquidity discounts [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 0.20 0.20  
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member] | Market multiples [Member] | Liquidity discounts [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [5],[6] 0.126 0.096  
Trading assets and private equity and debt investments [Member] | Foreign government, agency and municipal securities [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Fair Value, Financial Instrument, Assets ¥ 4 ¥ 6 3
Trading assets and private equity and debt investments [Member] | Foreign government, agency and municipal securities [Member] | DCF [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Interrelationships between valuation inputs [1] No predictable interrelationship No predictable interrelationship  
Trading assets and private equity and debt investments [Member] | Foreign government, agency and municipal securities [Member] | DCF [Member] | Credit spreads [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Lower fair value Lower fair value  
Trading assets and private equity and debt investments [Member] | Foreign government, agency and municipal securities [Member] | DCF [Member] | Credit spreads [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 0 0  
Trading assets and private equity and debt investments [Member] | Foreign government, agency and municipal securities [Member] | DCF [Member] | Credit spreads [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 0.023 0.024  
Trading assets and private equity and debt investments [Member] | Foreign government, agency and municipal securities [Member] | DCF [Member] | Credit spreads [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [5],[6] 0.011 0.011  
Trading assets and private equity and debt investments [Member] | Foreign government, agency and municipal securities [Member] | DCF [Member] | Recovery rates [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Higher fair value Higher fair value  
Trading assets and private equity and debt investments [Member] | Foreign government, agency and municipal securities [Member] | DCF [Member] | Recovery rates [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 0.125 0.034  
Trading assets and private equity and debt investments [Member] | Foreign government, agency and municipal securities [Member] | DCF [Member] | Recovery rates [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 0.18 0.18  
Trading assets and private equity and debt investments [Member] | Foreign government, agency and municipal securities [Member] | DCF [Member] | Recovery rates [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [5],[6] 0.172 0.144  
Trading assets and private equity and debt investments [Member] | Bank and corporate debt securities and loans for trading purposes [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Fair Value, Financial Instrument, Assets ¥ 104 ¥ 181 173
Trading assets and private equity and debt investments [Member] | Bank and corporate debt securities and loans for trading purposes [Member] | DCF [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Interrelationships between valuation inputs [1] No predictable interrelationship No predictable interrelationship  
Trading assets and private equity and debt investments [Member] | Bank and corporate debt securities and loans for trading purposes [Member] | DCF [Member] | Credit spreads [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Lower fair value Lower fair value  
Trading assets and private equity and debt investments [Member] | Bank and corporate debt securities and loans for trading purposes [Member] | DCF [Member] | Credit spreads [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 0.5 0  
Trading assets and private equity and debt investments [Member] | Bank and corporate debt securities and loans for trading purposes [Member] | DCF [Member] | Credit spreads [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 0.126 2.27  
Trading assets and private equity and debt investments [Member] | Bank and corporate debt securities and loans for trading purposes [Member] | DCF [Member] | Credit spreads [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [5],[6] 0.048 0.143  
Trading assets and private equity and debt investments [Member] | Bank and corporate debt securities and loans for trading purposes [Member] | DCF [Member] | Recovery rates [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Higher fair value Higher fair value  
Trading assets and private equity and debt investments [Member] | Bank and corporate debt securities and loans for trading purposes [Member] | DCF [Member] | Recovery rates [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 0 0  
Trading assets and private equity and debt investments [Member] | Bank and corporate debt securities and loans for trading purposes [Member] | DCF [Member] | Recovery rates [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 0.995 1  
Trading assets and private equity and debt investments [Member] | Bank and corporate debt securities and loans for trading purposes [Member] | DCF [Member] | Recovery rates [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [5],[6] 0.382 0.798  
Trading assets and private equity and debt investments [Member] | Commercial mortgage-backed securities ("CMBS") [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Fair Value, Financial Instrument, Assets ¥ 0 ¥ 10 0
Trading assets and private equity and debt investments [Member] | Commercial mortgage-backed securities ("CMBS") [Member] | DCF [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Interrelationships between valuation inputs [1]   No predictable interrelationship  
Trading assets and private equity and debt investments [Member] | Commercial mortgage-backed securities ("CMBS") [Member] | DCF [Member] | Yields [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2]   0.211  
Impact of increases in significant unobservable valuation inputs [3],[4]   Lower fair value  
Trading assets and private equity and debt investments [Member] | Commercial mortgage-backed securities ("CMBS") [Member] | DCF [Member] | Yields [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [5],[6]   0.211  
Trading assets and private equity and debt investments [Member] | Commercial mortgage-backed securities ("CMBS") [Member] | DCF [Member] | Loss severities [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2]   0.65  
Impact of increases in significant unobservable valuation inputs [3],[4]   Lower fair value  
Trading assets and private equity and debt investments [Member] | Commercial mortgage-backed securities ("CMBS") [Member] | DCF [Member] | Loss severities [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [5],[6]   0.65  
Trading assets and private equity and debt investments [Member] | Residential mortgage-backed securities ("RMBS") [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Fair Value, Financial Instrument, Assets ¥ 10 ¥ 48 35
Trading assets and private equity and debt investments [Member] | Residential mortgage-backed securities ("RMBS") [Member] | DCF [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Interrelationships between valuation inputs [1] No predictable interrelationship No predictable interrelationship  
Trading assets and private equity and debt investments [Member] | Residential mortgage-backed securities ("RMBS") [Member] | DCF [Member] | Yields [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 1.402    
Impact of increases in significant unobservable valuation inputs [3],[4] Lower fair value Lower fair value  
Trading assets and private equity and debt investments [Member] | Residential mortgage-backed securities ("RMBS") [Member] | DCF [Member] | Yields [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2]   0.215  
Trading assets and private equity and debt investments [Member] | Residential mortgage-backed securities ("RMBS") [Member] | DCF [Member] | Yields [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2]   0.622  
Trading assets and private equity and debt investments [Member] | Residential mortgage-backed securities ("RMBS") [Member] | DCF [Member] | Yields [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [5],[6] 1.402 0.416  
Trading assets and private equity and debt investments [Member] | Residential mortgage-backed securities ("RMBS") [Member] | DCF [Member] | Prepayment rates [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 0.12    
Impact of increases in significant unobservable valuation inputs [3],[4] Lower fair value Lower fair value  
Trading assets and private equity and debt investments [Member] | Residential mortgage-backed securities ("RMBS") [Member] | DCF [Member] | Prepayment rates [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2]   0.12  
Trading assets and private equity and debt investments [Member] | Residential mortgage-backed securities ("RMBS") [Member] | DCF [Member] | Prepayment rates [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2]   0.15  
Trading assets and private equity and debt investments [Member] | Residential mortgage-backed securities ("RMBS") [Member] | DCF [Member] | Prepayment rates [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [5],[6] 0.12 0.135  
Trading assets and private equity and debt investments [Member] | Residential mortgage-backed securities ("RMBS") [Member] | DCF [Member] | Loss severities [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Lower fair value Lower fair value  
Trading assets and private equity and debt investments [Member] | Residential mortgage-backed securities ("RMBS") [Member] | DCF [Member] | Loss severities [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 0 0  
Trading assets and private equity and debt investments [Member] | Residential mortgage-backed securities ("RMBS") [Member] | DCF [Member] | Loss severities [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 1 1  
Trading assets and private equity and debt investments [Member] | Residential mortgage-backed securities ("RMBS") [Member] | DCF [Member] | Loss severities [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [5],[6] 0.094 0.504  
Trading assets and private equity and debt investments [Member] | Real estate-backed securities [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Fair Value, Financial Instrument, Assets ¥ 82 ¥ 207 122
Trading assets and private equity and debt investments [Member] | Real estate-backed securities [Member] | DCF [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Interrelationships between valuation inputs [1] Not applicable Not applicable  
Trading assets and private equity and debt investments [Member] | Real estate-backed securities [Member] | DCF [Member] | Loss severities [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Lower fair value Lower fair value  
Trading assets and private equity and debt investments [Member] | Real estate-backed securities [Member] | DCF [Member] | Loss severities [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 0 0  
Trading assets and private equity and debt investments [Member] | Real estate-backed securities [Member] | DCF [Member] | Loss severities [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 0.175 0.169  
Trading assets and private equity and debt investments [Member] | Real estate-backed securities [Member] | DCF [Member] | Loss severities [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [5],[6] 0.005 0.023  
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Fair Value, Financial Instrument, Assets ¥ 34 ¥ 42 46
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member] | DCF [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Interrelationships between valuation inputs [1] Change in default probabilities typically accompanied by directionally similar change in loss severities and opposite change in prepayment rates Change in default probabilities typically accompanied by directionally similar change in loss severities and opposite change in prepayment rates  
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member] | DCF [Member] | Yields [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Lower fair value Lower fair value  
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member] | DCF [Member] | Yields [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 0.085 0.04  
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member] | DCF [Member] | Yields [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 0.407 0.50  
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member] | DCF [Member] | Yields [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [5],[6] 0.179 0.136  
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member] | DCF [Member] | Prepayment rates [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 0.20 0.20  
Impact of increases in significant unobservable valuation inputs [3],[4] Lower fair value Lower fair value  
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member] | DCF [Member] | Prepayment rates [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [5],[6] 0.20 0.20  
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member] | DCF [Member] | Default probabilities [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 0.02 0.02  
Impact of increases in significant unobservable valuation inputs [3],[4] Lower fair value Lower fair value  
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member] | DCF [Member] | Default probabilities [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [5],[6] 0.02 0.02  
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member] | DCF [Member] | Loss severities [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Lower fair value Lower fair value  
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member] | DCF [Member] | Loss severities [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 0.693 0.629  
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member] | DCF [Member] | Loss severities [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 1 1  
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member] | DCF [Member] | Loss severities [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [5],[6] 0.936 0.877  
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member] | DCF [Member] | Credit spreads [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 0.002    
Impact of increases in significant unobservable valuation inputs [3],[4] Lower fair value Lower fair value  
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member] | DCF [Member] | Credit spreads [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2]   0.001  
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member] | DCF [Member] | Credit spreads [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2]   0.169  
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member] | DCF [Member] | Credit spreads [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [5],[6] 0.002 0.047  
Trading assets and private equity and debt investments [Member] | Investment trust funds and other [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Fair Value, Financial Instrument, Assets ¥ 9 ¥ 3 3
Trading assets and private equity and debt investments [Member] | Investment trust funds and other [Member] | DCF [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Interrelationships between valuation inputs [1] Not applicable Not applicable  
Trading assets and private equity and debt investments [Member] | Investment trust funds and other [Member] | DCF [Member] | Liquidity discounts [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Lower fair value Lower fair value  
Trading assets and private equity and debt investments [Member] | Investment trust funds and other [Member] | DCF [Member] | Liquidity discounts [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 0.024 0.015  
Trading assets and private equity and debt investments [Member] | Investment trust funds and other [Member] | DCF [Member] | Liquidity discounts [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [2] 0.152 0.029  
Trading assets and private equity and debt investments [Member] | Investment trust funds and other [Member] | DCF [Member] | Liquidity discounts [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Trading assets and private equity and debt investments [5],[6] 0.055 0.021  
Equity contracts [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Fair Value, Financial Instrument, Assets [7] ¥ 27 ¥ 1 5
Equity contracts [Member] | Option models [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Interrelationships between valuation inputs [1] No predictable interrelationship No predictable interrelationship  
Equity contracts [Member] | Option models [Member] | Dividend yield [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Higher fair value Higher fair value  
Equity contracts [Member] | Option models [Member] | Dividend yield [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [2] 0 0  
Equity contracts [Member] | Option models [Member] | Dividend yield [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [2] 0.126 0.166  
Equity contracts [Member] | Option models [Member] | Dividend yield [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [5],[6]  
Equity contracts [Member] | Option models [Member] | Volatilities [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Higher fair value Higher fair value  
Equity contracts [Member] | Option models [Member] | Volatilities [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [2] 0.037 0.035  
Equity contracts [Member] | Option models [Member] | Volatilities [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [2] 1.009 0.994  
Equity contracts [Member] | Option models [Member] | Volatilities [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [5],[6]  
Equity contracts [Member] | Option models [Member] | Correlations [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Higher fair value Higher fair value  
Equity contracts [Member] | Option models [Member] | Correlations [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [2] (0.85) (0.85)  
Equity contracts [Member] | Option models [Member] | Correlations [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [2] 0.98 0.99  
Equity contracts [Member] | Option models [Member] | Correlations [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [5],[6]  
Interest rate contracts [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Fair Value, Financial Instrument, Assets [7] ¥ (16) ¥ 6 32
Interest rate contracts [Member] | DCF / Option models [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Interrelationships between valuation inputs [1] No predictable interrelationship No predictable interrelationship  
Interest rate contracts [Member] | DCF / Option models [Member] | Interest rates [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Higher fair value Higher fair value  
Interest rate contracts [Member] | DCF / Option models [Member] | Interest rates [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [2] 0.026 0.009  
Interest rate contracts [Member] | DCF / Option models [Member] | Interest rates [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [2] 0.05 0.045  
Interest rate contracts [Member] | DCF / Option models [Member] | Interest rates [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [5],[6]  
Interest rate contracts [Member] | DCF / Option models [Member] | Volatilities [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Higher fair value Higher fair value  
Interest rate contracts [Member] | DCF / Option models [Member] | Volatilities [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [2] 0.097 0.098  
Interest rate contracts [Member] | DCF / Option models [Member] | Volatilities [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [2] 0.13 0.133  
Interest rate contracts [Member] | DCF / Option models [Member] | Volatilities [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [5],[6]  
Interest rate contracts [Member] | DCF / Option models [Member] | Volatilities [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Higher fair value Higher fair value  
Interest rate contracts [Member] | DCF / Option models [Member] | Volatilities [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [2] 0.00424 0.0041  
Interest rate contracts [Member] | DCF / Option models [Member] | Volatilities [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [2] 0.01099 0.02617  
Interest rate contracts [Member] | DCF / Option models [Member] | Volatilities [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [5],[6]  
Interest rate contracts [Member] | DCF / Option models [Member] | Correlations [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Higher fair value Higher fair value  
Interest rate contracts [Member] | DCF / Option models [Member] | Correlations [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [2] (1) (1)  
Interest rate contracts [Member] | DCF / Option models [Member] | Correlations [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [2] 1 0.99  
Interest rate contracts [Member] | DCF / Option models [Member] | Correlations [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [5],[6]  
Credit contracts [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Fair Value, Financial Instrument, Assets [7] ¥ (56) ¥ (36) (46)
Credit contracts [Member] | DCF / Option models [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Interrelationships between valuation inputs [1] No predictable interrelationship No predictable interrelationship  
Credit contracts [Member] | DCF / Option models [Member] | Credit spreads [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Higher fair value Higher fair value  
Credit contracts [Member] | DCF / Option models [Member] | Credit spreads [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [2] 0 0  
Credit contracts [Member] | DCF / Option models [Member] | Credit spreads [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [2] 1.563 1.322  
Credit contracts [Member] | DCF / Option models [Member] | Credit spreads [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [5],[6]  
Credit contracts [Member] | DCF / Option models [Member] | Recovery rates [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Higher fair value Higher fair value  
Credit contracts [Member] | DCF / Option models [Member] | Recovery rates [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [2] 0.01 0.01  
Credit contracts [Member] | DCF / Option models [Member] | Recovery rates [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [2] 0.90 0.90  
Credit contracts [Member] | DCF / Option models [Member] | Recovery rates [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [5],[6]  
Credit contracts [Member] | DCF / Option models [Member] | Volatilities [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Higher fair value Higher fair value  
Credit contracts [Member] | DCF / Option models [Member] | Volatilities [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [2] 0.25 0.459  
Credit contracts [Member] | DCF / Option models [Member] | Volatilities [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [2] 0.816 0.519  
Credit contracts [Member] | DCF / Option models [Member] | Volatilities [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [5],[6]  
Credit contracts [Member] | DCF / Option models [Member] | Correlations [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Higher fair value Higher fair value  
Credit contracts [Member] | DCF / Option models [Member] | Correlations [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [2] 0.3 0  
Credit contracts [Member] | DCF / Option models [Member] | Correlations [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [2] 0.85 0.85  
Credit contracts [Member] | DCF / Option models [Member] | Correlations [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [5],[6]  
Foreign exchange contracts [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Fair Value, Financial Instrument, Assets [7] ¥ (22) ¥ (13) 3
Foreign exchange contracts [Member] | Option models [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Interrelationships between valuation inputs [1] No predictable interrelationship No predictable interrelationship  
Foreign exchange contracts [Member] | Option models [Member] | Interest rates [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Higher fair value    
Foreign exchange contracts [Member] | Option models [Member] | Interest rates [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [2] 0.031    
Foreign exchange contracts [Member] | Option models [Member] | Interest rates [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [2] 0.031    
Foreign exchange contracts [Member] | Option models [Member] | Interest rates [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [5],[6]    
Foreign exchange contracts [Member] | Option models [Member] | Volatilities [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Higher fair value Higher fair value  
Foreign exchange contracts [Member] | Option models [Member] | Volatilities [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [2] 0.014 0.016  
Foreign exchange contracts [Member] | Option models [Member] | Volatilities [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [2] 0.161 0.188  
Foreign exchange contracts [Member] | Option models [Member] | Volatilities [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [5],[6]  
Foreign exchange contracts [Member] | Option models [Member] | Correlations [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Higher fair value Higher fair value  
Foreign exchange contracts [Member] | Option models [Member] | Correlations [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [2] 0.24 0.29  
Foreign exchange contracts [Member] | Option models [Member] | Correlations [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [2] 0.7 0.7  
Foreign exchange contracts [Member] | Option models [Member] | Correlations [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Derivatives, net [5],[6]  
Loans and receivables [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Fair Value, Financial Instrument, Assets ¥ 584 ¥ 448 291
Loans and receivables [Member] | DCF [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Interrelationships between valuation inputs [1] No predictable interrelationship No predictable interrelationship  
Loans and receivables [Member] | DCF [Member] | Credit spreads [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Lower fair value Lower fair value  
Loans and receivables [Member] | DCF [Member] | Credit spreads [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Loans and receivables [2] 0 0  
Loans and receivables [Member] | DCF [Member] | Credit spreads [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Loans and receivables [2] 0.20 1.932  
Loans and receivables [Member] | DCF [Member] | Credit spreads [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Loans and receivables [5],[6] 0.059 0.099  
Loans and receivables [Member] | DCF [Member] | Recovery rates [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Higher fair value Higher fair value  
Loans and receivables [Member] | DCF [Member] | Recovery rates [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Loans and receivables [2] 0.645 0.667  
Loans and receivables [Member] | DCF [Member] | Recovery rates [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Loans and receivables [2] 1 1  
Loans and receivables [Member] | DCF [Member] | Recovery rates [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Loans and receivables [5],[6] 0.974 0.951  
Collateralized agreements [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Fair Value, Financial Instrument, Assets ¥ 16 ¥ 15 12
Collateralized agreements [Member] | DCF [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Interrelationships between valuation inputs [1] Not applicable Not applicable  
Collateralized agreements [Member] | DCF [Member] | Repo rate [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Collateralized agreements [2]   0.064  
Impact of increases in significant unobservable valuation inputs [3],[4] Lower fair value Lower fair value  
Collateralized agreements [Member] | DCF [Member] | Repo rate [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Collateralized agreements [2] 0.052    
Collateralized agreements [Member] | DCF [Member] | Repo rate [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Collateralized agreements [2] 0.056    
Collateralized agreements [Member] | DCF [Member] | Repo rate [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Collateralized agreements [5],[6] 0.054 0.064  
Non-trading debt securities [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Fair Value, Financial Instrument, Assets ¥ 48 ¥ 17 21
Non-trading debt securities [Member] | DCF [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Interrelationships between valuation inputs [1] Not applicable Not applicable  
Non-trading debt securities [Member] | DCF [Member] | Credit spreads [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Lower fair value Lower fair value  
Non-trading debt securities [Member] | DCF [Member] | Credit spreads [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Other assets [2] 0.041 0.052  
Non-trading debt securities [Member] | DCF [Member] | Credit spreads [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Other assets [2] 0.185 0.144  
Non-trading debt securities [Member] | DCF [Member] | Credit spreads [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Other assets [5],[6] 0.085 0.073  
Other [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Fair Value, Financial Instrument, Assets [8] ¥ 308 [9] ¥ 275 [9] 253
Other [Member] | DCF [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Interrelationships between valuation inputs [1],[8],[9] No predictable interrelationship No predictable interrelationship  
Other [Member] | DCF [Member] | WACC [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Other assets [2],[8],[9] 0.105 0.106  
Impact of increases in significant unobservable valuation inputs [3],[4],[8],[9] Lower fair value Lower fair value  
Other [Member] | DCF [Member] | WACC [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Other assets [5],[6],[8],[9] 0.105 0.106  
Other [Member] | DCF [Member] | Growth rates [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Other assets [2],[8],[9] 0.03 0.03  
Impact of increases in significant unobservable valuation inputs [3],[4],[8],[9] Higher fair value Higher fair value  
Other [Member] | DCF [Member] | Growth rates [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Other assets [5],[6],[8],[9] 0.03 0.03  
Other [Member] | DCF [Member] | Credit spreads [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4],[8],[9] Lower fair value    
Other [Member] | DCF [Member] | Credit spreads [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Other assets [2],[9] 0.003    
Other [Member] | DCF [Member] | Credit spreads [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Other assets [2],[9] 0.22    
Other [Member] | DCF [Member] | Credit spreads [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Other assets [5],[6],[9] 0.032    
Other [Member] | Market multiples [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Interrelationships between valuation inputs [1] Not applicable Not applicable  
Other [Member] | Market multiples [Member] | Liquidity discounts [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Other assets [2] 0.25 0.25  
Impact of increases in significant unobservable valuation inputs [3],[4] Lower fair value Lower fair value  
Other [Member] | Market multiples [Member] | Liquidity discounts [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Other assets [5],[6] 0.25 0.25  
Short-term borrowings [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Fair Value, Financial Instrument, Liabilities ¥ 43 ¥ 36 23
Short-term borrowings [Member] | DCF / Option models [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Interrelationships between valuation inputs [1] No predictable interrelationship No predictable interrelationship  
Short-term borrowings [Member] | DCF / Option models [Member] | Volatilities [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Higher fair value Higher fair value  
Short-term borrowings [Member] | DCF / Option models [Member] | Volatilities [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Short-term borrowings [2] 0.167 0.05  
Short-term borrowings [Member] | DCF / Option models [Member] | Volatilities [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Short-term borrowings [2] 0.602 0.515  
Short-term borrowings [Member] | DCF / Option models [Member] | Volatilities [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Short-term borrowings [5],[6]  
Short-term borrowings [Member] | DCF / Option models [Member] | Correlations [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Higher fair value Higher fair value  
Short-term borrowings [Member] | DCF / Option models [Member] | Correlations [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Short-term borrowings [2] (0.72) (0.72)  
Short-term borrowings [Member] | DCF / Option models [Member] | Correlations [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Short-term borrowings [2] 0.95 0.96  
Short-term borrowings [Member] | DCF / Option models [Member] | Correlations [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Short-term borrowings [5],[6]  
Payable and deposits [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Fair Value, Financial Instrument, Liabilities ¥ 12 ¥ 14 15
Payable and deposits [Member] | DCF / Option models [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Interrelationships between valuation inputs [1] No predictable interrelationship No predictable interrelationship  
Payable and deposits [Member] | DCF / Option models [Member] | Volatilities [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Higher fair value Higher fair value  
Payable and deposits [Member] | DCF / Option models [Member] | Volatilities [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Payables and deposits [2] 0.097 0.098  
Payable and deposits [Member] | DCF / Option models [Member] | Volatilities [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Payables and deposits [2] 0.108 0.106  
Payable and deposits [Member] | DCF / Option models [Member] | Volatilities [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Payables and deposits [5],[6]  
Payable and deposits [Member] | DCF / Option models [Member] | Correlations [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Higher fair value Higher fair value  
Payable and deposits [Member] | DCF / Option models [Member] | Correlations [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Payables and deposits [2] 0.4 0.4  
Payable and deposits [Member] | DCF / Option models [Member] | Correlations [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Payables and deposits [2] 0.97 0.98  
Payable and deposits [Member] | DCF / Option models [Member] | Correlations [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Payables and deposits [5],[6]  
Long-term borrowings [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Fair Value, Financial Instrument, Liabilities ¥ 452 ¥ 477 474
Long-term borrowings [Member] | DCF [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Interrelationships between valuation inputs [1] Not applicable Not applicable  
Long-term borrowings [Member] | DCF [Member] | Loss severities [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Lower fair value Lower fair value  
Long-term borrowings [Member] | DCF [Member] | Loss severities [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Long-term borrowings [2] 0.095 0.127  
Long-term borrowings [Member] | DCF [Member] | Loss severities [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Long-term borrowings [2] 0.993 0.995  
Long-term borrowings [Member] | DCF [Member] | Loss severities [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Long-term borrowings [5],[6] 0.544 0.798  
Long-term borrowings [Member] | DCF / Option models [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Interrelationships between valuation inputs [1] No predictable interrelationship No predictable interrelationship  
Long-term borrowings [Member] | DCF / Option models [Member] | Volatilities [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Higher fair value Higher fair value  
Long-term borrowings [Member] | DCF / Option models [Member] | Volatilities [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Long-term borrowings [2] 0.097 0.05  
Long-term borrowings [Member] | DCF / Option models [Member] | Volatilities [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Long-term borrowings [2] 0.602 0.515  
Long-term borrowings [Member] | DCF / Option models [Member] | Volatilities [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Long-term borrowings [5],[6]  
Long-term borrowings [Member] | DCF / Option models [Member] | Volatilities [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Higher fair value Higher fair value  
Long-term borrowings [Member] | DCF / Option models [Member] | Volatilities [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Long-term borrowings [2] 0.00655 0.00441  
Long-term borrowings [Member] | DCF / Option models [Member] | Volatilities [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Long-term borrowings [2] 0.00858 0.00679  
Long-term borrowings [Member] | DCF / Option models [Member] | Volatilities [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Long-term borrowings [5],[6]  
Long-term borrowings [Member] | DCF / Option models [Member] | Correlations [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Higher fair value Higher fair value  
Long-term borrowings [Member] | DCF / Option models [Member] | Correlations [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Long-term borrowings [2] (1) (1)  
Long-term borrowings [Member] | DCF / Option models [Member] | Correlations [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Long-term borrowings [2] 0.97 0.99  
Long-term borrowings [Member] | DCF / Option models [Member] | Correlations [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Long-term borrowings [5],[6]  
Other liabilities [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Fair Value, Financial Instrument, Liabilities ¥ 67 ¥ 65 ¥ 44
Other liabilities [Member] | DCF [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Interrelationships between valuation inputs [1] No predictable interrelationship No predictable interrelationship  
Other liabilities [Member] | DCF [Member] | Credit spreads [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Lower fair value Lower fair value  
Other liabilities [Member] | DCF [Member] | Credit spreads [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Other liabilities [2] 0.008 0.008  
Other liabilities [Member] | DCF [Member] | Credit spreads [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Other liabilities [2] 0.04 0.071  
Other liabilities [Member] | DCF [Member] | Credit spreads [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Other liabilities [5],[6] 0.008 0.01  
Other liabilities [Member] | DCF [Member] | Recovery rates [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Impact of increases in significant unobservable valuation inputs [3],[4] Higher fair value Higher fair value  
Other liabilities [Member] | DCF [Member] | Recovery rates [Member] | Minimum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Other liabilities [2] 0.91 0.91  
Other liabilities [Member] | DCF [Member] | Recovery rates [Member] | Maximum [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Other liabilities [2] 0.998 0.995  
Other liabilities [Member] | DCF [Member] | Recovery rates [Member] | Weighted Average [Member]      
Quantitative information about significant unobservable inputs [Line Items]      
Valuation inputs, Other liabilities [5],[6] 0.939 0.938  
[1] Consideration of the interrelationships between significant unobservable valuation inputs is only relevant where more than one unobservable valuation input is used to determine the fair value measurement of the financial instrument.
[2] Range information is provided in percentages, coefficients and multiples and represents the highest and lowest level significant unobservable valuation input used to value that type of financial instrument. A wide dispersion in the range does not necessarily reflect increased uncertainty or subjectivity in the valuation input and is typically just a consequence of the different characteristics of the financial instruments themselves.
[3] The above table only considers the impact of an increase in each significant unobservable valuation input on the fair value measurement of the financial instrument. However, a decrease in the significant unobservable valuation input would have the opposite effect on the fair value measurement of the financial instrument. For example, if an increase in a significant unobservable valuation input would result in a lower fair value measurement, a decrease in the significant unobservable valuation input would result in a higher fair value measurement.
[4] The impact of an increase in the significant unobservable valuation input on the fair value measurement for a derivative assumes Nomura is long risk to the input (such as being long volatility). Where Nomura is short such risk, the impact of an increase would have a converse effect on the fair value measurement of the derivative.
[5] Nomura has not provided weighted average information for derivatives as unlike cash products the risk on such products is distinct from the balance sheet value and is subject to netting. Discussion of the ranges of significant unobservable valuation inputs for derivatives and short-term and long-term borrowings which contain embedded derivatives classified in Level 3 is provided below as a substitute for weighted average information.
[6] Weighted average information for non-derivatives is calculated by weighting each valuation input by the fair value of the financial instrument.
[7] Derivatives which contain multiple types of risk are classified based on the primary risk type of the instrument.
[8] Includes non-financial assets carried at fair value on a recurring basis.
[9] Valuation techniques and unobservable valuation inputs in respect of equity securities reported within Other assets in the consolidated balance sheets.