Income Taxes (Expiry Schedule of Net Operating Loss Carryforwards) (Detail) ¥ in Millions	Mar. 31, 2020 JPY (¥)
Income Tax Disclosure [Abstract]
2021	¥ 12,549
2022	5,656
2023	8,847
2024	16,888
2025	10,882
Thereafter	90,681
Indefinite period	26,222
Total	¥ 171,725

Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32559-109319

Name:	us-gaap_OperatingLossCarryforwards
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant