Selling, General and Administrative Expenses (Summary of Selling, General and Administrative Expenses) (Detail) - JPY (¥) ¥ in Millions	6 Months Ended
Sep. 30, 2026	Sep. 30, 2025
Selling, General and Administrative Expense [Abstract]
Personnel expenses	¥ 252,485	¥ 190,939
IT-related Expenses	¥ 32,374	¥ 26,062

The amount of expense in the period for communications and data processing expense.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(4))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483621/220-10-S99-2

Name:	us-gaap_CommunicationsAndInformationTechnology
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration