Accumulated Other Comprehensive Income (Loss) - Summary of Changes in Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Unrealized gains (losses) on fair value option debt attributable to our own credit spread:
Balance at beginning of period		$ (24)	$ 0	$ (19)	$ 0
Cumulative effect adjustment to initially apply new accounting guidance for fair value option debt attributable to own credit spread, net of tax	[1]					$ (19)
Net (loss) arising during period, net of tax		(3)	0	(8)	0
Reclassification adjustment for losses realized in net income, net of tax	[2]	26	0	26	0
Total other comprehensive loss for period		23	0	18	0
Balance at end of period		(1)	0	(1)	0
Cumulative effect adjustment to initially apply new accounting guidance for fair value option debt attributable to credit, tax				(11)	0
Net (loss) arising during period, tax		(2)	0	(5)	0
Reclassification adjustment for gain (losses) realized in net income, tax		16	0	16	0
Unrealized gains (losses) on cash flow hedging instruments:
Balance at beginning of period				0	(15)
Net gains arising during period, net of tax				0	11
Reclassification adjustment for losses realized in net income, net of tax	[3]			0	4
Total other comprehensive income for period		0	0	0	15
Balance at end of period		0	0	0	0
Net gains arising during period, taxes				0	6
Reclassification adjustment for losses realized in net income, taxes				0	3
Pension and postretirement benefit plan liability:
Balance at beginning of period		14	26	24	29
Reclassification adjustment for gains realized in net income, net of tax	[4]			(10)	(3)
Total other comprehensive income for period		0	0	(10)	(3)
Balance at end of period		14	26	14	26
Reclassification adjustment for gains realized in net income, tax				(6)	(1)
Total accumulated other comprehensive income (loss) at end of period		$ 13	$ 26	13	26	$ 24
As Previously Reported [Member]
Unrealized gains (losses) on fair value option debt attributable to our own credit spread:
Balance at beginning of period				$ 0	$ 0

[1] For information on the adoption of new accounting guidance related to fair value option debt attributable to our own credit spread, see Note 13, "New Accounting Pronouncements."

[2] For the three and nine months ended September 30, 2017, the amounts reclassified are included as a component of loss on extinguishment of debt in our consolidated statement of income (loss).

[3] The amounts reclassified relate to currency swaps and are included as a component of interest expense in our consolidated statement of income (loss).

[4] The amounts reclassified are included as a component of salaries and employee benefits in our consolidated statement of income (loss).