Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net Income Attributable to MUAH	$ 1,073	$ 1,077	$ 990
Other Comprehensive Income (Loss), Net of Tax:
Net change in unrealized gains (losses) on cash flow hedges	(46)	(66)	(115)
Net change in unrealized gains (losses) on investment securities	(140)	16	(56)
Foreign currency translation adjustment	(2)	7	2
Pension and other postretirement benefit adjustments	(130)	95	23
Other Comprehensive Income Other, Net of Tax, Portion Attributable to Parent	(1)	0	0
Total other comprehensive income (loss)	(319)	52	(146)
Comprehensive Income (Loss) Attributable to MUAH	754	1,129	844
Comprehensive income (loss) from noncontrolling interests	24	43	68
Total Comprehensive Income (Loss)	$ 730	$ 1,086	$ 776