Business Segments (Details 2) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Business segments
Net interest income (expense)	$ 720	$ 719	$ 1,417	$ 1,402
Noninterest income (expense)	466	385	861	720
Total revenue	1,186	1,104	2,278	2,122
Noninterest expense	810	843	1,686	1,692
Provision for Loan and Lease Losses	(34)	26	124	23
Provision for credit losses	(37)	15	125	18
Income before income taxes and including noncontrolling interests	413	246	467	412
Income tax expense (benefit)	119	71	136	105
Net Income Including Noncontrolling Interests	294	175	331	307
Deduct: net loss from noncontrolling interests	11	6	23	11
Net Income Attributable to MUAH	305	181	354	318
Total assets, end of period	117,156	114,266	117,156	114,266	$ 116,216
Retail Banking and Wealth Markets | Operating segments
Business segments
Net interest income (expense)	478	473	959	951
Noninterest income (expense)	112	106	226	217
Total revenue	590	579	1,185	1,168
Noninterest expense	420	467	856	928
Provision for credit losses	(5)	6	(6)	12
Income before income taxes and including noncontrolling interests	175	106	335	228
Income tax expense (benefit)	51	26	97	45
Net Income Including Noncontrolling Interests	124	80	238	183
Net Income Attributable to MUAH	124	80	238	183
Total assets, end of period	63,467	61,468	63,467	61,468
Corporate Banking | Operating segments
Business segments
Net interest income (expense)	114	106	223	207
Noninterest income (expense)	38	41	66	73
Total revenue	152	147	289	280
Noninterest expense	49	48	98	100
Provision for credit losses	(28)	12	102	15
Income before income taxes and including noncontrolling interests	131	87	89	165
Income tax expense (benefit)	52	35	35	63
Net Income Including Noncontrolling Interests	79	52	54	102
Net Income Attributable to MUAH	79	52	54	102
Total assets, end of period	14,392	13,293	14,392	13,293
Transaction Banking | Operating segments
Business segments
Net interest income (expense)	120	111	241	227
Noninterest income (expense)	44	42	91	85
Total revenue	164	153	332	312
Noninterest expense	109	108	229	210
Provision for credit losses	(3)	0	(1)	1
Income before income taxes and including noncontrolling interests	58	45	104	101
Income tax expense (benefit)	23	18	41	39
Net Income Including Noncontrolling Interests	35	27	63	62
Net Income Attributable to MUAH	35	27	63	62
Total assets, end of period	1,838	1,779	1,838	1,779
Investment Banking & Markets | Operating segments
Business segments
Net interest income (expense)	60	62	119	122
Noninterest income (expense)	65	60	90	91
Total revenue	125	122	209	213
Noninterest expense	42	43	83	77
Provision for credit losses	2	(12)	32	(19)
Income before income taxes and including noncontrolling interests	81	91	94	155
Income tax expense (benefit)	12	23	(2)	35
Net Income Including Noncontrolling Interests	69	68	96	120
Net Income Attributable to MUAH	69	68	96	120
Total assets, end of period	11,762	11,277	11,762	11,277
Other | Operating segments
Business segments
Net interest income (expense)	(52)	(33)	(125)	(105)
Noninterest income (expense)	207	136	388	254
Total revenue	155	103	263	149
Noninterest expense	190	177	420	377
Provision for credit losses	(3)	9	(2)	9
Income before income taxes and including noncontrolling interests	(32)	(83)	(155)	(237)
Income tax expense (benefit)	(19)	(31)	(35)	(77)
Net Income Including Noncontrolling Interests	(13)	(52)	(120)	(160)
Deduct: net loss from noncontrolling interests	11	6	23	11
Net Income Attributable to MUAH	(2)	(46)	(97)	(149)
Total assets, end of period	$ 25,697	$ 26,449	$ 25,697	$ 26,449