Segment Reporting - Segment Result and Reconciliations to GAAP - Core Earnings Adjustments (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting, Revenue Reconciling Item [Line Items]
Net interest income (loss) after provisions for loan losses	$ 225	$ 186	$ 435	$ 427
Total other income (loss)	222	136	441	348
Goodwill and acquired intangible asset impairment and amortization	11	6	18	16
Income tax expense (benefit)	41	30	78	64
Net income (loss)	153	83	281	210
Total Adjustments [Member] | Adjustments [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Net interest income (loss) after provisions for loan losses	(3)	(21)	(17)	(23)
Total other income (loss)	(20)	(30)	(11)	3
Goodwill and acquired intangible asset impairment and amortization	11	6	18	16
Total Core Earnings adjustments to GAAP	(34)	(57)	(46)	(36)
Income tax expense (benefit)	(12)	(9)	(15)	(8)
Net income (loss)	(22)	(48)	(31)	(28)
Net Impact of Derivative Accounting [Member] | Total Adjustments [Member] | Adjustments [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Net interest income (loss) after provisions for loan losses	(3)	(21)	(17)	(23)
Total other income (loss)	(20)	(30)	(11)	3
Total Core Earnings adjustments to GAAP	(23)	(51)	(28)	(20)
Net Impact of Goodwill and Acquired Intangible Assets [Member] | Total Adjustments [Member] | Adjustments [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Goodwill and acquired intangible asset impairment and amortization	11	6	18	16
Total Core Earnings adjustments to GAAP	$ (11)	$ (6)	$ (18)	$ (16)