Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Statement of Comprehensive Income [Abstract]
Net Income (Loss) Attributable to MUAH	$ 311	$ 22	$ 690	$ (284)
Other Comprehensive Income (Loss), Net of Tax:
Net change in unrealized gains (losses) on cash flow hedges	(6)	34	(73)	360
Net change in unrealized gains (losses) on investment securities	186	179	(287)	437
Pension and other postretirement benefit adjustments	18	15	36	31
Other	(2)	0	(2)	0
Total other comprehensive (loss) income	196	228	(326)	828
Comprehensive (Loss) Income Attributable to MUAH	507	250	364	544
Comprehensive income (loss) from noncontrolling interests	(3)	(4)	(6)	(8)
Total Comprehensive (Loss) Income	$ 504	$ 246	$ 358	$ 536