Fair Value Measurements - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted average discount margin over LIBOR	7.00%
Securities issued by financial institutions and other entities backed by trust preferred securities at cost	$ 38		$ 42
Fair value of securities issued by financial institutions and other entities backed by trust preferred securities	62		63
Loans measured at fair value on nonrecurring basis	161	227	222
Change in fair value of nonrecurring fair value measured loans for charge-offs and impairment reserves	15	15
Assets taken in foreclosure of defaulted loans measured at fair value on a nonrecurring basis	11	19
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	100	158	173
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	$ 61	$ 69	$ 49
Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount margin over LIBOR	4.00%
Discount rates for fair value estimations	20.00%
Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount margin over LIBOR	11.00%
Discount rates for fair value estimations	75.00%