Business Segments (Details 2) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Business segments
Net interest income (expense)	$ 773	$ 723	$ 2,251	$ 2,162
Noninterest income (expense)	570	450	1,609	1,368
Total revenue	1,343	1,173	3,860	3,530
Noninterest expense	952	926	2,826	2,784
Provision for Loan and Lease Losses	68	23	190	45
Provision for credit losses	73	18	196	35
Income before income taxes and including noncontrolling interests	318	229	838	711
Income tax expense (benefit)	97	62	244	183
Net Income Including Noncontrolling Interests	221	167	594	528
Deduct: net loss from noncontrolling interests	39	21	62	32
Net Income Attributable to MUAH	260	188	656	560
Total assets, end of period	151,099	151,666	151,099	151,666	$ 153,070
Retail Banking and Wealth Markets | Operating segments
Business segments
Net interest income (expense)	481	479	1,427	1,421
Noninterest income (expense)	118	122	344	339
Total revenue	599	601	1,771	1,760
Noninterest expense	432	449	1,288	1,375
Provision for credit losses	23	(7)	17	5
Income before income taxes and including noncontrolling interests	144	159	466	380
Income tax expense (benefit)	40	44	130	97
Net Income Including Noncontrolling Interests	104	115	336	283
Net Income Attributable to MUAH	104	115	336	283
Total assets, end of period	63,340	60,828	63,340	60,828
Corporate Banking | Operating segments
Business segments
Net interest income (expense)	101	103	320	308
Noninterest income (expense)	122	32	188	105
Total revenue	223	135	508	413
Noninterest expense	53	62	150	164
Provision for credit losses	1	21	103	36
Income before income taxes and including noncontrolling interests	169	52	255	213
Income tax expense (benefit)	66	20	100	83
Net Income Including Noncontrolling Interests	103	32	155	130
Net Income Attributable to MUAH	103	32	155	130
Total assets, end of period	13,219	13,996	13,219	13,996
Transaction Banking | Operating segments
Business segments
Net interest income (expense)	125	109	350	326
Noninterest income (expense)	39	42	130	127
Total revenue	164	151	480	453
Noninterest expense	113	113	342	327
Provision for credit losses	1	0	0	1
Income before income taxes and including noncontrolling interests	50	38	138	125
Income tax expense (benefit)	20	15	54	49
Net Income Including Noncontrolling Interests	30	23	84	76
Net Income Attributable to MUAH	30	23	84	76
Total assets, end of period	1,908	1,836	1,908	1,836
Investment Banking & Markets | Operating segments
Business segments
Net interest income (expense)	49	59	170	182
Noninterest income (expense)	105	68	243	223
Total revenue	154	127	413	405
Noninterest expense	52	61	169	181
Provision for credit losses	23	(2)	53	(21)
Income before income taxes and including noncontrolling interests	79	68	191	245
Income tax expense (benefit)	22	13	16	40
Net Income Including Noncontrolling Interests	57	55	175	205
Deduct: net loss from noncontrolling interests			(1)
Net Income Attributable to MUAH	57	55	174	205
Total assets, end of period	14,354	14,155	14,354	14,155
MUFG Securities Americas [Member] | Operating segments
Business segments
Net interest income (expense)	46	17	106	52
Noninterest income (expense)	96	53	255	238
Total revenue	142	70	361	290
Noninterest expense	99	71	278	245
Provision for credit losses	0	0	0	0
Income before income taxes and including noncontrolling interests	43	(1)	83	45
Income tax expense (benefit)	17	0	33	18
Net Income Including Noncontrolling Interests	26	(1)	50	27
Net Income Attributable to MUAH	26	(1)	50	27
Total assets, end of period	30,526	33,697	30,526	33,697
Other | Operating segments
Business segments
Net interest income (expense)	(29)	(44)	(122)	(127)
Noninterest income (expense)	90	133	449	336
Total revenue	61	89	327	209
Noninterest expense	203	170	599	492
Provision for credit losses	25	6	23	14
Income before income taxes and including noncontrolling interests	(167)	(87)	(295)	(297)
Income tax expense (benefit)	(68)	(30)	(89)	(104)
Net Income Including Noncontrolling Interests	(99)	(57)	(206)	(193)
Deduct: net loss from noncontrolling interests	39	21	63	32
Net Income Attributable to MUAH	(60)	(36)	(143)	(161)
Total assets, end of period	$ 27,752	$ 27,154	$ 27,752	$ 27,154