Accumulated Other Comprehensive Loss - (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Unrealized gains (losses) on investment securities:
Balance at beginning of period		$ (234)		$ 158		$ (18)
Other comprehensive income for period:
Net unrealized gains (losses) arising during period, net of tax		(209)		(387)		244
Reclassification adjustment for gains realized in net income, net of tax	[1]	(44)		(30)		(74)
Amortization of net unrealized losses on securities transferred from available-for-sale to held-to-maturity realized in net income, net of tax	[2]	26		25		6
Total other comprehensive income (loss) for period		(227)		(392)		176
Balance at end of period		(461)		(234)		158
Unrealized losses on other-than-temporarily impaired debt securities held-to-maturity [Roll Forward]
Balance at beginning of period		0		0		(60)
Other comprehensive income for period:
Reclassification adjustment related to the accretion of unrealized other-than-temporary impairment, net of tax of $7 million(3)	[3]	0		0		9
Reclassification adjustment to reverse other-than-temporary impairment due to closure of VIE, net of tax of $36 million(3)		0		0		51
Total other comprehensive income for period		0		0		60
Balance at end of period		0		0		0
Unrealized (losses) gains on derivatives classified as cash flow hedges:
Balance at beginning of period		(170)		(156)		(83)
Other comprehensive income (loss) for period:
Net unrealized losses arising during period, net of tax		2		(21)		(77)
Reclassification adjustment of losses realized in net income, net of tax		11	[3]	7	[3]	4
Total other comprehensive income (loss) for period		13		(14)		(73)
Balance at end of period		(157)		(170)		(156)
Pension and postretirement benefit liability:
Balance at beginning of period		(3)		(3)		2
Other comprehensive income for period:
Change in unfunded pension and postretirement liability, net of tax		3		0		(5)
Total other comprehensive income (loss) for period		3		0		(5)
Balance at end of period		0		(3)		(3)
Total accumulated other comprehensive loss at end of period		$ (618)		$ (407)		(1)
AOCI included in pretax unrealized losses						$ 234

[1] Amount reclassified to net income is included in other securities gains, net in our consolidated statement of income.

[2] Amount amortized to net income is included in interest income in our consolidated statement of income. During 2014, we transferred securities from available-for-sale to held-to-maturity. At the date of transfer, AOCI included net pretax unrealized losses of $234 million related to the transferred securities which will be amortized over the remaining contractual life of each security as an adjustment of yield in a manner consistent with the amortization of any premium or discount.

[3] Amount reclassified to net income is included in interest income (expense) in our consolidated statement of income.