Fair Value Measurement- Summary of Carrying Amount of Hedged Financial Instruments, Related Notional Amount of Hedge and Estimated Fair Value of Derivatives (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Interest-bearing deposits with banks
Derivative [Line Items]
Carrying amount	$ 1,368	$ 1,396
Notional amount of hedge	1,368	1,396
Unrealized Gain	13	30
Unrealized (Loss)	(22)	(19)
Securities available-for-sale
Derivative [Line Items]
Carrying amount	6,328	5,914
Notional amount of hedge	6,774	6,647
Unrealized Gain	481	721
Unrealized (Loss)	(115)	(95)
Long-term debt
Derivative [Line Items]
Carrying amount	14,931	15,036
Notional amount of hedge	14,650	14,755
Unrealized Gain	460	483
Unrealized (Loss)	$ (57)	$ (72)