Business Segments (Details 2) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017		Mar. 31, 2016		Dec. 31, 2016
Business segments
Net interest income (expense)	[1]	$ 795		$ 724
Noninterest income (expense)	[1]	488		474
Total revenue	[1]	1,283		1,198
Noninterest expense	[1]	1,006		968
(Reversal of) provision for credit losses	[1]	(30)		162
Income before income taxes and including noncontrolling interests	[1]	307		68
Income tax expense (benefit)	[1]	83		18
Net Income Including Noncontrolling Interests	[1]	224		50
Deduct: net loss from noncontrolling interests	[1]	5		12
Net Income Attributable to MUAH	[1]	229		62
Total assets, end of period		149,678	[1]	156,554	[1]	$ 148,144
Operating segments | Regional Bank
Business segments
Net interest income (expense)	[1]	498		475
Noninterest income (expense)	[1]	112		114
Total revenue	[1]	610		589
Noninterest expense	[1]	502		441
(Reversal of) provision for credit losses	[1]	2		(2)
Income before income taxes and including noncontrolling interests	[1]	106		150
Income tax expense (benefit)	[1]	23		42
Net Income Including Noncontrolling Interests	[1]	83		108
Net Income Attributable to MUAH	[1]	83		108
Total assets, end of period	[1]	63,950		62,190
Operating segments | U.S. Wholesale Banking
Business segments
Net interest income (expense)	[1]	87		107
Noninterest income (expense)	[1]	104		29
Total revenue	[1]	191		136
Noninterest expense	[1]	53		49
(Reversal of) provision for credit losses	[1]	0		130
Income before income taxes and including noncontrolling interests	[1]	138		(43)
Income tax expense (benefit)	[1]	55		(17)
Net Income Including Noncontrolling Interests	[1]	83		(26)
Net Income Attributable to MUAH	[1]	83		(26)
Total assets, end of period	[1]	11,179		15,173
Operating segments | Transaction Banking
Business segments
Net interest income (expense)	[1]	137		113
Noninterest income (expense)	[1]	39		46
Total revenue	[1]	176		159
Noninterest expense	[1]	111		120
(Reversal of) provision for credit losses	[1]	0		2
Income before income taxes and including noncontrolling interests	[1]	65		37
Income tax expense (benefit)	[1]	26		14
Net Income Including Noncontrolling Interests	[1]	39		23
Net Income Attributable to MUAH	[1]	39		23
Total assets, end of period	[1]	2,094		2,522
Operating segments | Investment Banking & Markets
Business segments
Net interest income (expense)	[1]	42		56
Noninterest income (expense)	[1]	79		47
Total revenue	[1]	121		103
Noninterest expense	[1]	59		58
(Reversal of) provision for credit losses	[1]	(10)		31
Income before income taxes and including noncontrolling interests	[1]	72		14
Income tax expense (benefit)	[1]	(3)		(19)
Net Income Including Noncontrolling Interests	[1]	75		33
Deduct: net loss from noncontrolling interests	[1]			1
Net Income Attributable to MUAH	[1]	75		34
Total assets, end of period	[1]	13,778		14,556
Operating segments | MUSA
Business segments
Net interest income (expense)	[1]	59		25
Noninterest income (expense)	[1]	84		71
Total revenue	[1]	143		96
Noninterest expense	[1]	105		86
(Reversal of) provision for credit losses	[1]	0		0
Income before income taxes and including noncontrolling interests	[1]	38		10
Income tax expense (benefit)	[1]	15		4
Net Income Including Noncontrolling Interests	[1]	23		6
Net Income Attributable to MUAH	[1]	23		6
Total assets, end of period	[1]	30,472		32,961
Segment Reconciling Items
Business segments
Net interest income (expense)	[1]	(28)		(52)
Noninterest income (expense)	[1]	70		167
Total revenue	[1]	42		115
Noninterest expense	[1]	176		214
(Reversal of) provision for credit losses	[1]	(22)		1
Income before income taxes and including noncontrolling interests	[1]	(112)		(100)
Income tax expense (benefit)	[1]	(33)		(6)
Net Income Including Noncontrolling Interests	[1]	(79)		(94)
Deduct: net loss from noncontrolling interests	[1]	5		11
Net Income Attributable to MUAH	[1]	(74)		(83)
Total assets, end of period	[1]	$ 28,205		$ 29,152

[1] The transferred IHC entities are not measured using a "market view" perspective.