Carrying Value of Those Assets Measured at Fair Value on a Non-Recurring Basis (Detail) (USD $)	3 Months Ended								3 Months Ended																																3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended		3 Months Ended	12 Months Ended	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013 Loans Held-for-Sale Fair Value, Measurements, Nonrecurring [Member]	Dec. 31, 2012 Loans Held-for-Sale Fair Value, Measurements, Nonrecurring [Member]	Mar. 31, 2013 Loans Held For Investment [Member] Fair Value, Measurements, Nonrecurring [Member]	Dec. 31, 2012 Loans Held For Investment [Member] Fair Value, Measurements, Nonrecurring [Member]	Mar. 31, 2013 Other Real Estate Owned [Member] Fair Value, Measurements, Nonrecurring [Member]	Dec. 31, 2012 Other Real Estate Owned [Member] Fair Value, Measurements, Nonrecurring [Member]	Mar. 31, 2013 Affordable Housing [Member] Fair Value, Measurements, Nonrecurring [Member]	Mar. 31, 2012 Affordable Housing [Member] Fair Value, Measurements, Nonrecurring [Member]	Dec. 31, 2012 Affordable Housing [Member] Fair Value, Measurements, Nonrecurring [Member]	Mar. 31, 2013 Other Assets [Member] Fair Value, Measurements, Nonrecurring [Member]	Dec. 31, 2012 Other Assets [Member] Fair Value, Measurements, Nonrecurring [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 1 [Member] Loans Held-for-Sale Fair Value, Measurements, Nonrecurring [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 1 [Member] Loans Held-for-Sale Fair Value, Measurements, Nonrecurring [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 1 [Member] Loans Held For Investment [Member] Fair Value, Measurements, Nonrecurring [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 1 [Member] Loans Held For Investment [Member] Fair Value, Measurements, Nonrecurring [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 1 [Member] Other Real Estate Owned [Member] Fair Value, Measurements, Nonrecurring [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 1 [Member] Other Real Estate Owned [Member] Fair Value, Measurements, Nonrecurring [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 1 [Member] Affordable Housing [Member] Fair Value, Measurements, Nonrecurring [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 1 [Member] Other Assets [Member] Fair Value, Measurements, Nonrecurring [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 1 [Member] Other Assets [Member] Fair Value, Measurements, Nonrecurring [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 2 [Member] Loans Held-for-Sale Fair Value, Measurements, Nonrecurring [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 2 [Member] Loans Held-for-Sale Fair Value, Measurements, Nonrecurring [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 2 [Member] Loans Held For Investment [Member] Fair Value, Measurements, Nonrecurring [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 2 [Member] Loans Held For Investment [Member] Fair Value, Measurements, Nonrecurring [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 2 [Member] Other Real Estate Owned [Member] Fair Value, Measurements, Nonrecurring [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 2 [Member] Other Real Estate Owned [Member] Fair Value, Measurements, Nonrecurring [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 2 [Member] Affordable Housing [Member] Fair Value, Measurements, Nonrecurring [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 2 [Member] Other Assets [Member] Fair Value, Measurements, Nonrecurring [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 2 [Member] Other Assets [Member] Fair Value, Measurements, Nonrecurring [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 3 [Member] Loans Held-for-Sale Fair Value, Measurements, Nonrecurring [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member] Loans Held-for-Sale Fair Value, Measurements, Nonrecurring [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 3 [Member] Loans Held For Investment [Member] Fair Value, Measurements, Nonrecurring [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member] Loans Held For Investment [Member] Fair Value, Measurements, Nonrecurring [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 3 [Member] Other Real Estate Owned [Member] Fair Value, Measurements, Nonrecurring [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member] Other Real Estate Owned [Member] Fair Value, Measurements, Nonrecurring [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member] Affordable Housing [Member] Fair Value, Measurements, Nonrecurring [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 3 [Member] Other Assets [Member] Fair Value, Measurements, Nonrecurring [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member] Other Assets [Member] Fair Value, Measurements, Nonrecurring [Member]	Mar. 31, 2013 Valuation Allowance [Member] Loans Held-for-Sale Fair Value, Measurements, Nonrecurring [Member]	Dec. 31, 2012 Valuation Allowance [Member] Loans Held-for-Sale Fair Value, Measurements, Nonrecurring [Member]	Mar. 31, 2013 Valuation Allowance [Member] Loans Held For Investment [Member] Fair Value, Measurements, Nonrecurring [Member]	Dec. 31, 2012 Valuation Allowance [Member] Loans Held For Investment [Member] Fair Value, Measurements, Nonrecurring [Member]	Mar. 31, 2013 Valuation Allowance [Member] Other Real Estate Owned [Member] Fair Value, Measurements, Nonrecurring [Member]	Dec. 31, 2012 Valuation Allowance [Member] Other Real Estate Owned [Member] Fair Value, Measurements, Nonrecurring [Member]	Dec. 31, 2012 Valuation Allowance [Member] Affordable Housing [Member] Fair Value, Measurements, Nonrecurring [Member]	Mar. 31, 2013 Valuation Allowance [Member] Other Assets [Member] Fair Value, Measurements, Nonrecurring [Member]	Dec. 31, 2012 Valuation Allowance [Member] Other Assets [Member] Fair Value, Measurements, Nonrecurring [Member]	Mar. 31, 2013 Loans Held-for-Sale Mortgage Production Income [Member]	Mar. 31, 2013 Private Equity Partnership Investments [Member] Other Assets [Member] Fair Value, Measurements, Nonrecurring [Member]	Mar. 31, 2012 Private Equity Partnership Investments [Member] Other Assets [Member] Fair Value, Measurements, Nonrecurring [Member]	Mar. 31, 2013 Repossessed Personal Property [Member] Other Assets [Member] Fair Value, Measurements, Nonrecurring [Member]	Mar. 31, 2012 Repossessed Personal Property [Member] Other Assets [Member] Fair Value, Measurements, Nonrecurring [Member]	Mar. 31, 2013 Property Subject to Operating Lease [Member] Other Assets [Member] Fair Value, Measurements, Nonrecurring [Member]	Mar. 31, 2012 Property Subject to Operating Lease [Member] Other Assets [Member] Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain (Loss) on Sales of Loans, Net	$ 4,000,000	$ 13,000,000																																																$ 3,000,000
Assets, Fair Value Disclosure			68,000,000	65,000,000	5,000,000	308,000,000	224,000,000	264,000,000			82,000,000	32,000,000	65,000,000	0	0	0	0	0	0	0	0	0	68,000,000	65,000,000	0	0	214,000,000	205,000,000	0	32,000,000	42,000,000	0	0	5,000,000	308,000,000	10,000,000	59,000,000	82,000,000	0	23,000,000
Asset Impairment Charges									$ 0	$ 0																															$ 0	$ 0	$ 0	$ 79,000,000	$ 12,000,000	$ 48,000,000	$ 96,000,000	$ 4,000,000	$ 13,000,000		$ 0	$ 0	$ 4,000,000	$ 1,000,000	$ 0	$ 1,000,000