v3.26.1
Investment Securities - Schedule of Investments in Listed Equity Instruments at Fair Value through Other Comprehensive Income (Detail) - JPY (¥)
¥ in Millions
Mar. 31, 2026
Mar. 31, 2025
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income ¥ 5,505,439 ¥ 5,170,856
Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 4,013,893 3,745,559
TOYOTA MOTOR CORPORATION [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 461,665 381,946
Ares Management Corporation [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 294,031 369,498
Jefferies Financial Group Inc. [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 242,909 294,857
Fujikura Ltd. [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 171,854 37,802
SBI Holdings, Inc. [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 153,846 107,541
The Bank of East Asia, Limited [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 139,104 0
DAIKIN INDUSTRIES, LTD. [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 130,795 121,050
ITOCHU Corporation [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 95,763 69,010
Sumitomo Realty & Development Co., Ltd. [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 89,351 65,841
MITSUI & CO., LTD. [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 76,475 53,891
TOYOTA TSUSHO CORPORATION [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 75,855 31,783
Seven & i Holdings Co., Ltd. [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 62,644 63,809
KUBOTA CORPORATION [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 62,045 53,040
East Japan Railway Company [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 59,552 48,495
DAIWA HOUSE INDUSTRY CO., LTD. [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 55,485 59,690
Central Japan Railway Company [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 42,882 29,967
NIPPON STEEL CORPORATION [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 37,688 41,818
Sumitomo Electric Industries Ltd [Member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 36,835 10,840
Sanwa Holdings Corporation [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 35,504 51,752
Shionogi & Co., Ltd. [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 33,482 21,678
KAJIMA CORPORATION [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 31,742 20,067
SG HOLDINGS CO., LTD. [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 30,679 31,042
Makita Corporation [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 29,449 28,567
Mitsui O.S.K. Lines, Ltd. [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 29,232 34,241
West Japan Railway Company [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 28,027 26,132
Murata Manufacturing Co., Ltd. [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 27,391 18,525
TORAY INDUSTRIES, INC. [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 26,436 24,406
MINEBEA MITSUMI Inc. [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 25,917 22,221
DAIFUKU CO., LTD. [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 24,893 22,293
NIDEC CORPORATION [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 23,848 30,228
CME Group Inc. [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 22,284 18,718
Mitsui Fudosan Co., Ltd. [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 22,110 32,083
GMO Payment Gateway, Inc. [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 20,523 19,823
The Kansai Electric Power Company, Incorporated [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 20,133 13,808
Kawasaki Heavy Industries, Ltd. [Member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 19,429 11,975
TOYO SUISAN KAISHA, LTD.[member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 19,373 15,488
ASAHI KASEI CORPORATION [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 17,965 18,223
TOHO GAS CO., LTD. [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 16,640 13,666
Maruichi Steel Tube Ltd. [Member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 15,012 12,980
Marubeni Corporation [Member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 14,784 12,523
MEIDENSHA CORPORATION [Member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 14,640 8,423
BROTHER INDUSTRIES, LTD. [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 14,284 14,544
KANEKA CORPORATION [Member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 14,084 11,773
YAMAZAKI BAKING CO LTD [Member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 13,994 11,366
IBIDEN CO., LTD. [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 13,768 9,208
OASAKA GAS CO., LTD. | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 13,689 7,257
Sumitomo Metal Mining Co., Ltd. [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 13,568 6,218
KOITO MANUFACTURING CO., LTD. [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 13,275 10,001
TBS HOLDINGS, INC. [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 13,227 15,203
Electric Power Development Co., LTD. [Member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 13,024 7,977
BANDAI NAMCO Holdings Inc. [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 13,001 16,823
BLUE ZONES HOLDINGS CO LTD [Member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 12,260 11,877
Rengo Co., LTD. | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 12,157 7,660
CTBC Financial Holding Co Ltd | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 12,027 8,335
Sotetsu Holdings, Inc. [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 11,985 8,963
Chubu Electric Power Company, Incorporated [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 11,576 10,914
FUJIFILM Holdings Corporation [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 1,047 12,036
Sekisui House, Ltd. [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 965 15,330
Japan Exchange Group, Inc. [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income 350 36,066
Others [member] | Listed [member]    
Disclosure of detailed information about financial instruments [line items]    
Equity instruments at fair value through other comprehensive income ¥ 977,340 ¥ 1,174,268