BUSINESS SEGMENT AND FOREIGN INFORMATION - Yen/Dollar Exchange Rates Used (Detail) $ in Millions		12 Months Ended
		Dec. 31, 2021 USD ($) ¥ / $	Dec. 31, 2020 USD ($) ¥ / $	Dec. 31, 2019 USD ($) ¥ / $
Segment Reporting, Other Significant Reconciling Item [Line Items]
Weighted-average yen/dollar exchange rate | ¥ / $	[1]	109.79	106.86	109.07
Yen percent strengthening (weakening)		(2.70%)	2.10%	1.20%
Exchange effect on pretax operating earnings (in millions)		$ (47)	$ 38	$ 20
Yen/dollar exchange rate at December 31 | ¥ / $	[1]	115.02	103.50
Yen percent strengthening (weakening)		(10.00%)	5.90%
Exchange effect on total assets
Segment Reporting, Other Significant Reconciling Item [Line Items]
Exchange effect		$ (9,635)	$ 7,970
Exchange effect on total liabilities
Segment Reporting, Other Significant Reconciling Item [Line Items]
Exchange effect		$ (7,566)	$ 7,870

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