Accumulated Other Comprehensive Loss - (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016		Jan. 01, 2018	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of new accounting principle in period of adoption	[1]			$ 0		$ 0		$ 91
Unrealized gains (losses) on investment securities:
Balance at beginning of period		$ (299)		(461)		(234)
Other comprehensive income for period:
Net unrealized gains (losses) arising during period, net of tax		(215)		227		(209)
Reclassification adjustment for (gains) losses realized in net income, net of tax	[2]	(18)		(33)		(44)
Amortization of net unrealized losses on securities transferred from available-for-sale to held-to-maturity realized in net income, net of tax		13	[3]	17	[3]	26	[4]
Total other comprehensive income (loss) for period		(220)		211		(227)
Balance at end of period		(519)		(299)		(461)
Unrealized gains (losses) on fair value option liabilities attributable to our own credit spread:
Balance at beginning of period		(23)		174		0
Other comprehensive income (loss) for period:
Net unrealized gains (losses) arising during period, net of tax		324		(193)		0
Total other comprehensive income (loss) for period		324		(193)		0
Balance at end of period		301		(23)		174
Unrealized gains (losses) on derivatives designated as cash flow hedges:
Balance at beginning of period		(199)		(157)		(170)
Other comprehensive income (loss) for period:
Net unrealized gains (losses) arising during period, net of tax		22		(18)		2
Reclassification adjustment for (gains) losses realized in net income, net of tax		18	[4]	11	[4]	11	[5]
Total other comprehensive income (loss) for period		40		(7)		13
Balance at end of period		(159)		(199)		(157)
Pension and postretirement benefit liability:
Balance at beginning of period		3		0		(3)
Change in unfunded pension and postretirement liability, net of tax		8		2		3
Total other comprehensive income for period		8		2		3
Balance at end of period		11		3		0
Total accumulated other comprehensive loss at end of period		(366)		(431)		(618)
Accounting Standards Update 2016-01, Equity Investments Previously Classified as Available-for-sale [Member] | Unrealized Gains (Losses) on Investment Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of new accounting principle in period of adoption	[6]			4		0			$ 0
Accounting Standards Update 2018-02 [Member] | Unrealized Gains (Losses) on Investment Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of new accounting principle in period of adoption	[6]			(53)		0			0
Accounting Standards Update 2018-02 [Member] | Unrealized Gains (Losses) on Fair Value Option Liabilities Attributable to Our Own Credit Spread [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of new accounting principle in period of adoption	[6]			(4)		0			0
Accounting Standards Update 2018-02 [Member] | Unrealized Gains (Losses) on Investment Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of new accounting principle in period of adoption	[6]			(35)		0			0
Accounting Standards Update 2018-02 [Member] | Pension and Postretirement Benefit Liability [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of new accounting principle in period of adoption	[6]			1		0			0
Accounting Standards Update 2016-01, Fair Value Option [Member] | Unrealized Gains (Losses) on Fair Value Option Liabilities Attributable to Our Own Credit Spread [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of new accounting principle in period of adoption	[5]			0		174			$ 0
As Previously Reported [Member]
Unrealized gains (losses) on investment securities:
Balance at beginning of period		(250)		(461)		(234)
Other comprehensive income for period:
Balance at end of period				(250)		(461)
Unrealized gains (losses) on fair value option liabilities attributable to our own credit spread:
Balance at beginning of period		(19)		0		0
Other comprehensive income (loss) for period:
Balance at end of period				(19)		0
Unrealized gains (losses) on derivatives designated as cash flow hedges:
Balance at beginning of period		(164)		(157)		(170)
Other comprehensive income (loss) for period:
Balance at end of period				(164)		(157)
Pension and postretirement benefit liability:
Balance at beginning of period		$ 2		0		(3)
Balance at end of period				$ 2		$ 0

[1] See Note 2, "Summary of Significant Accounting Polices and New Accounting Pronouncements," for additional discussion.

[2] Amount reclassified to net income (loss) is included in other securities gains, net in our consolidated statement of income (loss).

[3] Amount amortized to net income (loss) is included in interest income in our consolidated statement of income (loss). During 2014, we transferred securities from available-for-sale to held-to-maturity. At the date of transfer, AOCI included net pretax unrealized losses related to the transferred securities which are being 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.

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

[5] See Note 2, "Summary of Significant Accounting Polices and New Accounting Pronouncements," for additional discussion.

[6] As a result of adopting new accounting guidance in 2017, beginning January 1, 2017, the fair value movement on fair value option liabilities attributable to our own credit spread is recorded in common equity as a component of other comprehensive income (loss).