- Changes in the Carrying Amount of Goodwill (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020
Goodwill [Line Items]
Goodwill, Transfers			$ 0
Goodwill, Impairment Loss	$ (357)	$ (1,614)	(357)	$ (1,614)
Goodwill, Gross					$ 3,378
Goodwill [Roll Forward]
Goodwill, December 31, 2019			1,764
Accumulated impairment losses					(1,971)
Goodwill, end of period	1,407		1,407
Balance at September 30, 2020	1,407		1,407		1,407
Operating segments | Regional Bank
Goodwill [Line Items]
Goodwill, Transfers			0
Goodwill, Impairment Loss			(87)
Goodwill, Gross					2,193
Goodwill [Roll Forward]
Goodwill, December 31, 2019			770
Accumulated impairment losses					1,510
Goodwill, end of period	683		683
Balance at September 30, 2020	683		683		683
Operating segments | Global Corporate & Investment Banking - U.S.
Goodwill [Line Items]
Goodwill, Transfers			86
Goodwill, Impairment Loss			(270)
Goodwill, Gross					944
Goodwill [Roll Forward]
Goodwill, December 31, 2019			667
Accumulated impairment losses					461
Goodwill, end of period	483		483
Balance at September 30, 2020	483		483		483
Operating segments | Transaction Banking
Goodwill [Line Items]
Goodwill, Transfers			(86)
Goodwill, Impairment Loss			0
Goodwill, Gross					165
Goodwill [Roll Forward]
Goodwill, December 31, 2019			251
Accumulated impairment losses					0
Goodwill, end of period	165		165
Balance at September 30, 2020	165		165		165
Operating segments | MUFG Fund Services [Member]
Goodwill [Line Items]
Goodwill, Transfers			0
Goodwill, Impairment Loss			0
Goodwill, Gross					76
Goodwill [Roll Forward]
Goodwill, December 31, 2019			76
Accumulated impairment losses					0
Goodwill, end of period	76		76
Balance at September 30, 2020	$ 76		$ 76		$ 76