Summary of Significant Accounting Policies, Nature of Operations and Other Developments- Changes in Accounting Policy (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2013
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other assets	$ 4,961		$ 4,961		$ 4,630
Other liabilities	2,060		2,060		1,897
Retained earnings	8,786		8,786		8,283	$ 7,458
Other	120	$ 106	347	$ 281
Income before income taxes and including noncontrolling interests	229	330	641	891
Income tax expense	64	88	169	242
Net Income Attributable to MUAH	$ 186	247	$ 504	663
Scenario, Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other assets					4,685
Other liabilities					1,889
Retained earnings					8,346	7,512
Other		128		337
Income before income taxes and including noncontrolling interests		308		835
Income tax expense		67		179
Net Income Attributable to MUAH		246		670
Scenario, Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other assets					(55)
Other liabilities					8
Retained earnings					$ (63)	$ (54)
Other		(22)		(56)
Income before income taxes and including noncontrolling interests		22		56
Income tax expense		21		63
Net Income Attributable to MUAH		$ 1		$ (7)