Commitments and Contingencies (Summary of Maximum Potential Amount of Future Payments of Certain Guarantees Classified Based on Internal Ratings) (Detail) - Performance guarantees, Guarantees on loans, Guarantees on securities and Other guarantees - JPY (¥) ¥ in Billions		Mar. 31, 2020	Mar. 31, 2019
Guarantor Obligations [Line Items]
Maximum potential/Contractual or Notional amount		¥ 5,181	¥ 5,065
Investment grade
Guarantor Obligations [Line Items]
Maximum potential/Contractual or Notional amount	[1]	4,233	4,124
Non-investment grade
Guarantor Obligations [Line Items]
Maximum potential/Contractual or Notional amount		¥ 948	¥ 941

[1] Investment grade in the internal rating scale generally corresponds to BBB- or above in the external rating scale.