Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Minimum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Discount rates for fair value estimations	15.00%
Maximum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Discount rates for fair value estimations	90.00%
Significant Unobservable Inputs (Level 3) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Change in fair value of nonrecurring fair value measured loans for charge-offs and impairment reserves	$ 42	$ 27
Fair Value, Measurements, Nonrecurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Loans measured at fair value on nonrecurring basis	210	226	$ 293
Assets taken in foreclosure of defaulted loans measured at fair value on a nonrecurring basis	32	62
Fair Value, Measurements, Nonrecurring [Member] | 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	88	127	153
Fair Value, Measurements, Nonrecurring [Member] | 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	$ 122	$ 99	$ 140