Investment in Securities (Total Other-Than-Temporary Impairment with Offset for Amount of Total Other-Than-Temporary Impairment Recognized in Other Comprehensive Income (Loss)) (Detail) - JPY (¥) ¥ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Total other-than-temporary impairment losses	¥ 0	¥ 1,359	¥ 1,246
Portion of loss recognized in other comprehensive income (before taxes)	0	(136)	0
Net impairment losses recognized in earnings	¥ 0	¥ 1,223	¥ 1,246