v3.26.1
Variable Interest Entities and Securitizations (Consolidated Assets of Consolidated VIEs as well as Total Assets and Maximum Exposure to Loss for Significant Unconsolidated VIEs) (Detail) - JPY (¥)
¥ in Millions
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2024
Variable Interest Entity [Line Items]      
Total assets of MHFG ¥ 294,895,707 ¥ 276,741,152 ¥ 272,173,200
Significant unconsolidated VIEs- Maximum exposure to loss 2,070,000 1,521,000  
Consolidated VIEs      
Variable Interest Entity [Line Items]      
Total assets of MHFG 13,428,079 11,810,404  
Unconsolidated VIEs      
Variable Interest Entity [Line Items]      
Total assets of MHFG 7,955,000 5,823,000  
Asset-backed commercial paper/loan programs      
Variable Interest Entity [Line Items]      
Significant unconsolidated VIEs- Maximum exposure to loss 0 0  
Asset-backed commercial paper/loan programs | Consolidated VIEs      
Variable Interest Entity [Line Items]      
Total assets of MHFG 2,252,000 3,387,000  
Asset-backed commercial paper/loan programs | Unconsolidated VIEs      
Variable Interest Entity [Line Items]      
Total assets of MHFG 0 0  
Asset-backed securitizations      
Variable Interest Entity [Line Items]      
Significant unconsolidated VIEs- Maximum exposure to loss 96,000 100,000  
Asset-backed securitizations | Consolidated VIEs      
Variable Interest Entity [Line Items]      
Total assets of MHFG 3,457,000 1,609,000  
Asset-backed securitizations | Unconsolidated VIEs      
Variable Interest Entity [Line Items]      
Total assets of MHFG 183,000 181,000  
Investments in securitization products      
Variable Interest Entity [Line Items]      
Significant unconsolidated VIEs- Maximum exposure to loss 0 0  
Investments in securitization products | Consolidated VIEs      
Variable Interest Entity [Line Items]      
Total assets of MHFG 382,000 384,000  
Investments in securitization products | Unconsolidated VIEs      
Variable Interest Entity [Line Items]      
Total assets of MHFG 0 0  
Investment funds      
Variable Interest Entity [Line Items]      
Significant unconsolidated VIEs- Maximum exposure to loss 1,974,000 1,421,000  
Investment funds | Consolidated VIEs      
Variable Interest Entity [Line Items]      
Total assets of MHFG 2,246,000 1,562,000  
Investment funds | Unconsolidated VIEs      
Variable Interest Entity [Line Items]      
Total assets of MHFG 7,773,000 5,642,000  
Trust arrangements and other      
Variable Interest Entity [Line Items]      
Significant unconsolidated VIEs- Maximum exposure to loss 0 0  
Trust arrangements and other | Consolidated VIEs      
Variable Interest Entity [Line Items]      
Total assets of MHFG 5,090,000 4,869,000  
Trust arrangements and other | Unconsolidated VIEs      
Variable Interest Entity [Line Items]      
Total assets of MHFG ¥ 0 ¥ 0