Fair Value Measurements - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of independent pricing sources used to value privately issued mortgage-backed securities valued with internal modeling	2		2		2
Privately issued mortgage-backed securities at cost					$ 1,100,000,000
Weighted-average reliance on internal model pricing, percentage			33.00%
Average weighting placed on the values provided by the independent sources, percentage			67.00%
Weighted average discount margin over LIBOR			8.00%
Securities issued by financial institutions and other entities backed by trust preferred securities at cost	43,000,000		43,000,000		43,000,000
Fair value of securities issued by financial institutions and other entities backed by trust preferred securities	59,000,000		59,000,000		62,000,000
OTTI losses				5,000,000
Loans measured at fair value on nonrecurring basis	247,000,000	320,000,000	247,000,000	320,000,000
Change in fair value of nonrecurring fair value measured loans for charge-offs and impairment reserves	33,000,000	17,000,000	82,000,000	47,000,000
Nonrecurring fair value measurement	20,000,000	51,000,000	20,000,000	51,000,000
Significant Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans measured at fair value on nonrecurring basis	163,000,000	221,000,000	163,000,000	221,000,000
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans measured at fair value on nonrecurring basis	$ 84,000,000	$ 99,000,000	$ 84,000,000	$ 99,000,000
Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount margin over LIBOR	5.00%		5.00%
Discount rates for fair value estimations			10.00%
Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount margin over LIBOR	11.00%		11.00%
Discount rates for fair value estimations			80.00%