Fair Value Measurements - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 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	60,000,000		60,000,000		62,000,000
OTTI losses		1,000,000		5,000,000
Loans measured at fair value on nonrecurring basis	254,000,000	344,000,000	254,000,000	344,000,000
Change in fair value of nonrecurring fair value measured loans for charge-offs and impairment reserves	34,000,000	21,000,000	69,000,000	34,000,000
Nonrecurring fair value measurement	15,000,000	47,000,000	15,000,000	47,000,000
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	167,000,000	234,000,000	167,000,000	234,000,000
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	$ 87,000,000	$ 110,000,000	$ 87,000,000	$ 110,000,000
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	10.00%		10.00%
Discount rates for fair value estimations			80.00%