Correction of Prior Period Amounts (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013	Dec. 31, 2012
Net interest income
Interest expense-deposits	$ 61	$ 61	$ 123	$ 121
Noninterest income
Trading account activities	14	21	30	26
Brokerage commissions and fees	13	11	26	22
Income before income taxes and including noncontrolling interests	307	174	527	368
Net Income Attributable to MUFG Americas Holdings Corporation (MUAH)	249	142	424	290
Affected line items on the Consolidated Balance Sheet and Statements of Changes in Stockholder's Equity:
Retained earnings	7,936		7,936		7,512	6,845
As Previously Reported
Net interest income
Interest expense-deposits		67		132
Noninterest income
Trading account activities		24		32
Brokerage commissions and fees		12		24
Income before income taxes and including noncontrolling interests		172		365
Net Income Attributable to MUFG Americas Holdings Corporation (MUAH)		141		288
Affected line items on the Consolidated Balance Sheet and Statements of Changes in Stockholder's Equity:
Retained earnings						6,875
Error pertaining to income of certificate of deposits recognized within noninterest income | Adjustment
Net interest income
Interest expense-deposits		(6)		(11)
Noninterest income
Trading account activities		(3)		(6)
Brokerage commissions and fees		(1)		(2)
Income before income taxes and including noncontrolling interests		2		3
Net Income Attributable to MUFG Americas Holdings Corporation (MUAH)		1		2
Affected line items on the Consolidated Balance Sheet and Statements of Changes in Stockholder's Equity:
Retained earnings						$ (30)