Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net (Loss) Income Attributable to MUAH	$ (734)	$ 1,073	$ 1,077
Other Comprehensive Income (Loss), Net of Tax:
Net change in unrealized gains (losses) on cash flow hedges	105	(46)	(66)
Net change in unrealized gains (losses) on investment securities	280	(140)	16
Foreign currency translation adjustment	0	(2)	7
Pension and other postretirement benefit adjustments	76	(130)	95
Other Comprehensive Income Other, Net of Tax, Portion Attributable to Parent	1	(1)	0
Total other comprehensive income (loss)	462	(319)	52
Comprehensive Income (Loss) Attributable to MUAH	(272)	754	1,129
Comprehensive income (loss) from noncontrolling interests	17	24	43
Total Comprehensive Income (Loss)	$ (289)	$ 730	$ 1,086