Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement of Comprehensive Income [Abstract]
Net Income Attributable to MUAH	$ 184	$ 166
Other Comprehensive Income (Loss), Net of Tax:
Net change in unrealized gains (losses) on cash flow hedges	24	(58)
Net change in unrealized gains (losses) on investment securities	152	(190)
Foreign currency translation adjustment	0	(2)
Pension and other postretirement benefit adjustments	6	10
Other	1	(1)
Total other comprehensive income (loss)	183	(241)
Comprehensive Income (Loss) Attributable to MUAH	367	(75)
Comprehensive income (loss) from noncontrolling interests	(5)	1
Total Comprehensive Income (Loss)	$ 362	$ (74)