Business Segments and Revenue from Contracts with Customers - Segment Results and Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Net interest income (loss)	$ 6,156	$ 5,555	$ 17,721	$ 17,040
Non-interest income (loss)	1,674	1,826	4,596	4,146
Total net revenue (loss)	7,830	7,381	22,317	21,186
Provision (benefit) for credit losses	(342)	331	(2,325)	10,000
Non-interest expense	4,186	3,548	11,892	11,047
Income from continuing operations before income taxes	3,986	3,502	12,750	139
Income tax provision (benefit)	882	1,096	2,782	(10)
Income (loss) from continuing operations, net of tax	3,104	2,406	9,968	149
Total loans held for investment	261,390	248,223	261,390	248,223	$ 251,624
Total Deposits	305,938	305,725	305,938	305,725	$ 305,442
Uncollectible portion of billed finance charges and fees	123	235	478	942
Operating segments | Credit Card
Segment Reporting Information [Line Items]
Net interest income (loss)	3,620	3,292	10,209	10,363
Non-interest income (loss)	1,263	1,013	3,545	2,769
Total net revenue (loss)	4,883	4,305	13,754	13,132
Provision (benefit) for credit losses	(198)	450	(1,325)	7,096
Non-interest expense	2,424	2,003	6,822	6,180
Income from continuing operations before income taxes	2,657	1,852	8,257	(144)
Income tax provision (benefit)	627	438	1,952	(34)
Income (loss) from continuing operations, net of tax	2,030	1,414	6,305	(110)
Total loans held for investment	105,030	103,641	105,030	103,641
Total Deposits	0	0	0	0
Operating segments | Consumer Banking
Segment Reporting Information [Line Items]
Net interest income (loss)	2,159	1,904	6,290	5,226
Non-interest income (loss)	127	107	412	330
Total net revenue (loss)	2,286	2,011	6,702	5,556
Provision (benefit) for credit losses	(91)	(43)	(523)	1,693
Non-interest expense	1,186	1,011	3,426	3,038
Income from continuing operations before income taxes	1,191	1,043	3,799	825
Income tax provision (benefit)	282	247	897	195
Income (loss) from continuing operations, net of tax	909	796	2,902	630
Total loans held for investment	77,112	68,688	77,112	68,688
Total Deposits	252,387	249,684	252,387	249,684
Operating segments | Commercial Banking
Segment Reporting Information [Line Items]
Net interest income (loss)	578	517	1,558	1,526
Non-interest income (loss)	306	237	803	655
Total net revenue (loss)	884	754	2,361	2,181
Provision (benefit) for credit losses	(53)	(74)	(475)	1,209
Non-interest expense	459	424	1,295	1,261
Income from continuing operations before income taxes	478	404	1,541	(289)
Income tax provision (benefit)	113	95	364	(69)
Income (loss) from continuing operations, net of tax	365	309	1,177	(220)
Total loans held for investment	79,248	75,894	79,248	75,894
Total Deposits	43,347	36,783	43,347	36,783
Other
Segment Reporting Information [Line Items]
Net interest income (loss)	(201)	(158)	(336)	(75)
Non-interest income (loss)	(22)	469	(164)	392
Total net revenue (loss)	(223)	311	(500)	317
Provision (benefit) for credit losses	0	(2)	(2)	2
Non-interest expense	117	110	349	568
Income from continuing operations before income taxes	(340)	203	(847)	(253)
Income tax provision (benefit)	(140)	316	(431)	(102)
Income (loss) from continuing operations, net of tax	(200)	(113)	(416)	(151)
Total loans held for investment	0	0	0	0
Total Deposits	$ 10,204	$ 19,258	$ 10,204	$ 19,258