Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement of Comprehensive Income [Abstract]
Net (Loss) Income Attributable to MUAH	$ 121	$ (1,372)	$ (163)	$ (989)
Other Comprehensive Income (Loss), Net of Tax:
Net change in unrealized gains (losses) on cash flow hedges	(15)	50	345	130
Net change in unrealized gains (losses) on investment securities	47	53	484	351
Pension and other postretirement benefit adjustments	16	7	47	19
Other	0	0	0	1
Total other comprehensive income (loss)	48	110	876	501
Comprehensive Income (Loss) Attributable to MUAH	169	(1,262)	713	(488)
Comprehensive income (loss) from noncontrolling interests	(4)	(4)	(12)	(12)
Total Comprehensive Income (Loss)	$ 165	$ (1,266)	$ 701	$ (500)