Business Segments - Schedule of Segments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Business segments
Net interest income (expense)	$ 2,815	$ 2,862	$ 2,716
Noninterest income	1,530	1,123	876
Total income	4,345	3,985	3,592
Other expense	3,438	2,823	2,713
(Reversal of) provision for credit losses	228	6	(29)
Income before income taxes and including noncontrolling interests	679	1,156	908
Income tax benefit	151	359	279
Net Income including Noncontrolling Interests	528	797	629
Deduct: Net loss from noncontrolling interests	45	19	18
Net Income Attributable to MUAH	573	816	647
Total assets, end of period	116,206	113,623	105,849
Reconciling Items
Business segments
Net interest income (expense)	(374)	(361)	(329)
Noninterest income	(188)	(230)	(210)
Total income	(562)	(591)	(539)
Other expense	(176)	(154)	(123)
(Reversal of) provision for credit losses	(2)	(5)	1
Income before income taxes and including noncontrolling interests	(384)	(432)	(417)
Income tax benefit	(151)	(170)	(163)
Net Income including Noncontrolling Interests	(233)	(262)	(254)
Net Income Attributable to MUAH	(233)	(262)	(254)
Total assets, end of period	(2,313)	(2,229)	(1,632)
Regional Bank [Member] [Domain] | Operating segments
Business segments
Net interest income (expense)	1,934	2,088	1,981
Noninterest income	450	440	471
Total income	2,384	2,528	2,452
Other expense	1,677	1,596	1,662
(Reversal of) provision for credit losses	14	(2)	(35)
Income before income taxes and including noncontrolling interests	693	934	825
Income tax benefit	200	305	271
Net Income including Noncontrolling Interests	493	629	554
Net Income Attributable to MUAH	493	629	554
Total assets, end of period	60,743	62,234	56,777
US Corporate Banking | Operating segments
Business segments
Net interest income (expense)	409	362	316
Noninterest income	135	177	161
Total income	544	539	477
Other expense	167	154	127
(Reversal of) provision for credit losses	206	(17)	20
Income before income taxes and including noncontrolling interests	171	402	330
Income tax benefit	66	158	130
Net Income including Noncontrolling Interests	105	244	200
Net Income Attributable to MUAH	105	244	200
Total assets, end of period	14,841	12,985	10,218
Transaction Banking | Operating segments
Business segments
Net interest income (expense)	465	443	447
Noninterest income	169	158	161
Total income	634	601	608
Other expense	410	361	357
(Reversal of) provision for credit losses	1	(3)	(3)
Income before income taxes and including noncontrolling interests	223	243	254
Income tax benefit	87	95	100
Net Income including Noncontrolling Interests	136	148	154
Net Income Attributable to MUAH	136	148	154
Total assets, end of period	2,122	1,780	1,575
Investment Banking & Markets | Operating segments
Business segments
Net interest income (expense)	245	268	268
Noninterest income	182	285	229
Total income	427	553	497
Other expense	137	131	120
(Reversal of) provision for credit losses	(22)	38	1
Income before income taxes and including noncontrolling interests	312	384	376
Income tax benefit	72	104	112
Net Income including Noncontrolling Interests	240	280	264
Net Income Attributable to MUAH	240	280	264
Total assets, end of period	11,897	10,892	9,438
Other | Operating segments
Business segments
Net interest income (expense)	136	62	33
Noninterest income	782	293	64
Total income	918	355	97
Other expense	1,223	735	570
(Reversal of) provision for credit losses	31	(5)	(13)
Income before income taxes and including noncontrolling interests	(336)	(375)	(460)
Income tax benefit	(123)	(133)	(171)
Net Income including Noncontrolling Interests	(213)	(242)	(289)
Deduct: Net loss from noncontrolling interests	45	19	18
Net Income Attributable to MUAH	(168)	(223)	(271)
Total assets, end of period	$ 28,916	$ 27,961	$ 29,473