Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net Income Attributable to MUAH	$ 1,077	$ 990	$ 644
Other Comprehensive Income, Net of Tax:
Net change in unrealized gains (losses) on cash flow hedges	(66)	(115)	12
Net change in unrealized gains (losses) on investment securities	16	(56)	(6)
Foreign currency translation adjustment	7	2	(14)
Pension and other postretirement benefit adjustments	95	23	(13)
Total other comprehensive income (loss)	52	(146)	(21)
Comprehensive Income Attributable to MUAH	1,129	844	623
Comprehensive loss from noncontrolling interests	43	68	45
Total Comprehensive Income	$ 1,086	$ 776	$ 578