v3.26.1
Regulatory requirements - Additional information (Detail)
¥ in Millions
Mar. 31, 2026
JPY (¥)
Mar. 31, 2026
USD ($)
Mar. 31, 2025
JPY (¥)
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]      
Common equity Tier 1 capital ratio 0.0769 0.0769  
Tier 1 capital ratio 9.19% 9.19%  
Consolidated Capital adequacy ratio 0.1119 0.1119  
Quantified total of business risk 1.20 1.20 1.20
Segregated client cash recognized as an asset in Deposits with stock exchanges and other segregated cash | ¥ ¥ 166,651   ¥ 110,223
Segregated securities recognized as assets in Trading assets and Collateralized agreements | ¥ ¥ 960,952   ¥ 1,034,783
NSC [Member]      
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]      
Quantified total of business risk 1.20 1.20 1.20
NFPS [Member]      
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]      
Quantified total of business risk 1.20 1.20 1.20
NSI [Member]      
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]      
Net capital defined under the alternative method   $ 1,000,000  
Percentage of total risk margin requirement 8.00% 8.00%  
Amount of maintenance of net capital as cash   $ 1,000,000  
Minimum net capital percentage of SEC risk margin amount 2.00% 2.00%  
NGFP [Member]      
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]      
Net capital defined under the alternative method   $ 20,000,000  
Minimum net capital percentage of SEC risk margin amount 2.00% 2.00%  
Minimum net capital percentage of CFTC risk margin amount 2.00% 2.00%  
ILLC [Member]      
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]      
Net capital defined under the alternative method   $ 1,000,000  
Ratio of net capital under the alternative method 2.00% 2.00%  
Minimum capital required   $ 45,000