Long-Term Debt - Summary of Long Term Debt (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Long-term debt	$ 5,540	$ 6,684
UnionBanCal Corporation [Member]
Debt Instrument [Line Items]
Long-term debt	804	413
Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	4,736	6,271
Senior debt [Member] | Fixed rate 3.50% notes due June 2022 [Member] | UnionBanCal Corporation [Member]
Debt Instrument [Line Items]
Long-term debt	397
Senior debt [Member] | Fixed and floating rate Federal Home Loan Bank advances with maturities ranging from January 2013 to February 2016 [Member] | Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	2,100	3,625
Senior debt [Member] | Floating rate notes due March 2012 [Member] | Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt		500
Senior debt [Member] | Floating rate notes due June 2014 [Member] | Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	300	300
Senior debt [Member] | Fixed rate 2.125% notes due December 2013 [Member] | Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	399	399
Senior debt [Member] | Fixed rate 3.00% notes due June 2016 [Member] | Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	699	698
Senior debt [Member] | Fixed rate 2.125% notes due June 2017 [Member] | Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	499
Subordinated debt [Member] | Fixed rate 5.25% notes due December 2013 [Member] | UnionBanCal Corporation [Member]
Debt Instrument [Line Items]
Long-term debt	407	413
Subordinated debt [Member] | Fixed rate 5.95% notes due May 2016 [Member] | Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	731	741
Note Payable [Member] | Fixed rate 6.03% notes due July 2014 (related to consolidated VIE) [Member] | Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	$ 8	$ 8