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 Billions	Mar. 31, 2020	Mar. 31, 2019
Variable Interest Entity [Line Items]
Consolidated VIEs- Consolidated assets	¥ 5,815	¥ 6,048
Significant unconsolidated VIEs- Total assets	2,376	1,350
Significant unconsolidated VIEs- Maximum exposure to loss	521	418
Asset-backed commercial paper/loan programs
Variable Interest Entity [Line Items]
Consolidated VIEs- Consolidated assets	2,160	2,249
Asset-backed securitizations
Variable Interest Entity [Line Items]
Consolidated VIEs- Consolidated assets	572	571
Significant unconsolidated VIEs- Total assets	77	70
Significant unconsolidated VIEs- Maximum exposure to loss	7	8
Investments in securitization products
Variable Interest Entity [Line Items]
Consolidated VIEs- Consolidated assets	370	372
Investment funds
Variable Interest Entity [Line Items]
Consolidated VIEs- Consolidated assets	2,694	2,836
Significant unconsolidated VIEs- Total assets	2,299	1,280
Significant unconsolidated VIEs- Maximum exposure to loss	514	410
Trust arrangements and other
Variable Interest Entity [Line Items]
Consolidated VIEs- Consolidated assets	¥ 19	¥ 20