BUSINESS SEGMENT AND SELECTED FOREIGN CURRENCY TRANSLATION ITEMS - Yen/Dollar Exchange Rates Used (Detail) $ in Millions		12 Months Ended
		Dec. 31, 2024 USD ($) ¥ / $	Dec. 31, 2023 USD ($) ¥ / $	Dec. 31, 2022 USD ($) ¥ / $
Segment Reporting, Other Significant Reconciling Item [Line Items]
Weighted-average yen/dollar exchange rate | ¥ / $	[1]	150.97	140.57	130.17
Yen percent strengthening (weakening)		(6.90%)	(7.40%)	(15.70%)
Exchange effect on pretax operating earnings (in millions)		$ (125)	$ (131)	$ (318)
Yen/dollar exchange rate at December 31 | ¥ / $	[1]	158.18	141.83
Yen percent strengthening (weakening)		(10.30%)	(6.40%)
Exchange effect on total assets
Segment Reporting, Other Significant Reconciling Item [Line Items]
Exchange effect		$ (6,127)	$ (3,984)
Exchange effect on total liabilities
Segment Reporting, Other Significant Reconciling Item [Line Items]
Exchange effect		$ (9,624)	$ (6,936)

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