BUSINESS SEGMENT AND SELECTED FOREIGN CURRENCY TRANSLATION ITEMS - Yen/Dollar Exchange Rates Used (Detail) $ in Millions		12 Months Ended
		Dec. 31, 2023 USD ($) ¥ / $	Dec. 31, 2022 USD ($) ¥ / $	Dec. 31, 2021 USD ($) ¥ / $
Segment Reporting, Other Significant Reconciling Item [Line Items]
Weighted-average yen/dollar exchange rate | ¥ / $	[1]	140.57	130.17	109.79
Yen percent strengthening (weakening)		(7.40%)	(15.70%)	(2.70%)
Exchange effect on pretax operating earnings (in millions)		$ (131)	$ (318)	$ (43)
Yen/dollar exchange rate at December 31 | ¥ / $	[1]	141.83	132.70
Yen percent strengthening (weakening)		(6.40%)	(13.30%)
Exchange effect on total assets
Segment Reporting, Other Significant Reconciling Item [Line Items]
Exchange effect		$ (3,984)	$ (11,099)
Exchange effect on total liabilities
Segment Reporting, Other Significant Reconciling Item [Line Items]
Exchange effect		$ (6,936)	$ (9,513)

[1] Rates are based on the published MUFG Bank, Ltd. telegraphic transfer middle rate (TTM)