Summary of Significant Accounting Policies and Nature of Operations Summary of Significant Accounting Policies, Nature of Operations and Other Developments- Changes in Accounting Policy (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Other assets	$ 5,377	$ 4,630
Other liabilities	2,023	1,897
Retained earnings	8,854	8,283	$ 7,458
Other Noninterest Expense	362	283	304
Total, Fair Value	6,823	4,426
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Noncontrolling Interest	679	1,156	908
Income tax expense	151	359	279
Net Income Attributable to MUAH	$ 573	816	647
Scenario, Previously Reported [Member]
Other assets		4,685
Other liabilities		1,889
Retained earnings		8,346	7,512
Other Noninterest Expense		359	368
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Noncontrolling Interest		1,080	844
Income tax expense		274	195
Net Income Attributable to MUAH		825	667
Scenario, Adjustment [Member]
Other assets		(55)
Other liabilities		8
Retained earnings		(63)	(54)
Other Noninterest Expense		(76)	(64)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Noncontrolling Interest		76	64
Income tax expense		85	84
Net Income Attributable to MUAH		$ (9)	$ (20)