Related Party Transactions (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended			0 Months Ended	1 Months Ended	3 Months Ended	12 Months Ended						12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Oct. 01, 2011 BTMU	Sep. 30, 2008 BTMU	Dec. 31, 2013 BTMU	Dec. 31, 2013 BTMU	Dec. 31, 2012 BTMU	Dec. 31, 2011 BTMU	Dec. 31, 2013 Bank	Dec. 31, 2012 Bank	Jun. 30, 2013 Bank Union Bank, N.A. and other subsidiaries Floating rate subordinated debt due December 2023	Dec. 31, 2013 UnionBanCal Corporation	Dec. 31, 2012 UnionBanCal Corporation	Dec. 31, 2013 UnionBanCal Corporation Subordinated Debt Floating rate subordinated debt due December 2023	Dec. 31, 2013 UnionBanCal Corporation Union Bank, N.A. and other subsidiaries Floating rate subordinated debt due December 2023
Related Party Transaction [Line Items]
Unsecured revolving credit facility with BTMU					$ 500
Unsecured revolving credit facility years					3 years
Unsecured revolving credit facility amount outstanding						0	0
Risk-weighted assets						14.61%	14.61%	13.34%		14.91%	13.17%
Project Related expenditure							19	39	42
Common equity contribution received	1,200		618			1,200							1,200
Debt issued	6,547	5,622										750	763	869	300	300
Increase in assets				990
Short term borrowing	2,563	1,363		38
Capital contribution from BTMU				783
Derivative notional amount						735	735	415
Net unrealized losses on derivatives							7	10
Noninterest income	876	818	827				33	21	18
Noninterest expense	2,793	2,566	2,415				13	18	12
Reimbursements for facility and staff arrangements							31
Amount of overdraft balance outstanding						$ 0	$ 0	$ 0