Loans (Impaired Loans Information) (Parenthetical) (Detail) - JPY (¥) ¥ in Millions		Mar. 31, 2020	Mar. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investment	[1]	¥ 716,204	¥ 646,132
Small balance homogeneous loans of which were collectively evaluated for impairment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investment		¥ 260,596	¥ 257,099

[1] These impaired loans do not require an allowance for loan losses because the MHFG Group has sufficient collateral to cover probable loan losses.