Selected Quarterly Financial Data (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Net interest income	$ 507	$ 503	$ 540	$ 562	$ 586	$ 559	$ 555	$ 552	$ 2,112		$ 2,252		$ 2,273
Provision for credit losses	(3)	94	46	58	23	20	(45)	(71)	195		(73)		(165)
Net interest income after provision for credit losses	510	409	494	504	563	539	600	623	1,917		2,325		2,438
Total other revenues	542	486	436	390	363	486	537	513	1,854	[1]	1,899	[1]	2,002	[1]
Operating expenses	871	1,106	774	750	780	790	786	1,282	3,501		3,638		3,391
Income (loss) before income tax	181	(211)	156	144	146	235	351	(146)	270		586		1,049
Income tax expense (benefit)	48	39	35	35	34	58	82	92	157		266		1,228
Net income (loss)	$ 133	$ (250)	$ 121	$ 109	$ 112	$ 177	$ 269	$ (238)	$ 113		$ 320		$ (179)

[1] See Note 24, "Business Segments," for a reconciliation of total other revenues on a U.S. GAAP basis to other operating income for each business segment under the Group Reporting Basis.