Summary of Significant Accounting Policies, Nature of Operations and Other Developments- Changes in Accounting Policy (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015	Dec. 31, 2014
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other assets	$ 6,188		$ 6,188		$ 5,387	$ 4,640
Other liabilities	2,262		2,262		2,017	1,891
Retained earnings	9,189		9,189		8,836	8,265
Other	81	$ 96	179	$ 170
Income before income taxes and including noncontrolling interests	413	246	467	412
Income tax expense	119	71	136	105
Net Income Attributable to MUAH	$ 305	$ 181	$ 354	$ 318
Scenario, Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other assets					5,377	4,630
Other liabilities					2,023	1,897
Retained earnings					$ 8,854	$ 8,283