Long-Term Debt - Summary of Long-Term Debt (Parenthetical) (Detail)							6 Months Ended												0 Months Ended	6 Months Ended
	Jun. 30, 2013 UnionBanCal Fixed rate 3.50% notes due June 2022 [Member] Senior debt [Member]	Dec. 31, 2012 UnionBanCal Fixed rate 3.50% notes due June 2022 [Member] Senior debt [Member]	Jun. 30, 2013 UnionBanCal Fixed rate 5.25% notes due December 2013 [Member] Subordinated Debt [Member]	Dec. 31, 2012 UnionBanCal Fixed rate 5.25% notes due December 2013 [Member] Subordinated Debt [Member]	Jun. 30, 2013 Subsidiaries [Member] Federal Home Loan Bank advances [Member] Senior debt [Member]	Dec. 31, 2012 Subsidiaries [Member] Federal Home Loan Bank advances [Member] Senior debt [Member]	Jun. 30, 2013 Subsidiaries [Member] Floating rate notes due June 2014 [Member] Senior debt [Member]	Dec. 31, 2012 Subsidiaries [Member] Floating rate notes due June 2014 [Member] Senior debt [Member]	Jun. 30, 2013 Subsidiaries [Member] Fixed rate 2.125% notes due December 2013 [Member] Senior debt [Member]	Dec. 31, 2012 Subsidiaries [Member] Fixed rate 2.125% notes due December 2013 [Member] Senior debt [Member]	Jun. 30, 2013 Subsidiaries [Member] Fixed rate 3.00% notes due June 2016 [Member] Senior debt [Member]	Dec. 31, 2012 Subsidiaries [Member] Fixed rate 3.00% notes due June 2016 [Member] Senior debt [Member]	Jun. 30, 2013 Subsidiaries [Member] Fixed rate 2.125% notes due June 2017 [Member] Senior debt [Member]	Dec. 31, 2012 Subsidiaries [Member] Fixed rate 2.125% notes due June 2017 [Member] Senior debt [Member]	Jun. 30, 2013 Subsidiaries [Member] Fixed rate 6.03% notes due July 2014 (related to consolidated VIE) [Member] Note payable [Member]	Dec. 31, 2012 Subsidiaries [Member] Fixed rate 6.03% notes due July 2014 (related to consolidated VIE) [Member] Note payable [Member]	Jun. 30, 2013 Subsidiaries [Member] Fixed rate 5.95% notes due May 2016 [Member] Subordinated Debt [Member]	Dec. 31, 2012 Subsidiaries [Member] Fixed rate 5.95% notes due May 2016 [Member] Subordinated Debt [Member]	Jun. 28, 2013 Subsidiaries [Member] Floating rate notes due June 2023 Subordinated Debt [Member]	Jun. 30, 2013 Subsidiaries [Member] Floating rate notes due June 2023 Subordinated Debt [Member]	Jun. 30, 2013 Subsidiaries [Member] Floating rate [Member] Junior subordinated debt payable to trusts [Member]	Dec. 31, 2012 Subsidiaries [Member] Floating rate [Member] Junior subordinated debt payable to trusts [Member]	Jun. 30, 2013 Subsidiaries [Member] Capital Lease Obligations [Member] Junior subordinated debt payable to trusts [Member]	Dec. 31, 2012 Subsidiaries [Member] Capital Lease Obligations [Member] Junior subordinated debt payable to trusts [Member]
Debt Instrument [Line Items]
Debt instrument, Fixed interest rate	3.50%	3.50%	5.25%	5.25%					2.125%	2.125%	3.00%	3.00%	2.125%	2.125%	6.03%	6.03%	5.95%	5.95%
Interest rate above 3-month LIBOR							0.95%	0.95%											1.20%	1.20%
Debt instrument, weighted-average interest rate					1.32%	1.39%	1.23%	1.26%												1.48%	2.62%	2.66%	4.88%	4.72%
Variable interest rate							three-month LIBOR												three-month LIBOR	three-month LIBOR