Business Segments - Schedule of Segment Results and Reconciliation (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Net interest income	$ 22,460	$ 20,873	$ 18,834
Non-interest income	4,777	4,628	4,579
Total net revenue	27,237	25,501	23,413
Provision for loan, lease and other losses	7,551	6,459	4,536
Total non-interest expense	14,194	13,558	12,996
Income from continuing operations before income taxes	5,492	5,484	5,881
Income tax provision (benefit)	3,375	1,714	1,869
Income from continuing operations, net of tax	2,117	3,770	4,012
Loans held for investment	254,473	245,586	229,851
Total deposits	$ 243,702	$ 236,768	$ 217,721
Effective income tax rate	35.00%	35.00%	35.00%
Operating Segments | Credit Card
Segment Reporting Information [Line Items]
Net interest income	$ 13,648	$ 12,635	$ 11,161
Non-interest income	3,325	3,380	3,421
Total net revenue	16,973	16,015	14,582
Provision for loan, lease and other losses	6,066	4,926	3,417
Total non-interest expense	7,916	7,703	7,502
Income from continuing operations before income taxes	2,991	3,386	3,663
Income tax provision (benefit)	1,071	1,226	1,309
Income from continuing operations, net of tax	1,920	2,160	2,354
Loans held for investment	114,762	105,552	96,125
Total deposits	0	0	0
Operating Segments | Consumer Banking
Segment Reporting Information [Line Items]
Net interest income	6,380	5,829	5,755
Non-interest income	749	733	710
Total net revenue	7,129	6,562	6,465
Provision for loan, lease and other losses	1,180	1,055	819
Total non-interest expense	4,233	4,139	4,026
Income from continuing operations before income taxes	1,716	1,368	1,620
Income tax provision (benefit)	626	498	586
Income from continuing operations, net of tax	1,090	870	1,034
Loans held for investment	75,078	73,054	70,372
Total deposits	185,842	181,917	172,702
Operating Segments | Commercial Banking
Segment Reporting Information [Line Items]
Net interest income	2,261	2,216	1,865
Non-interest income	708	578	487
Total net revenue	2,969	2,794	2,352
Provision for loan, lease and other losses	301	483	302
Total non-interest expense	1,603	1,407	1,156
Income from continuing operations before income taxes	1,065	904	894
Income tax provision (benefit)	389	329	324
Income from continuing operations, net of tax	676	575	570
Loans held for investment	64,575	66,916	63,266
Total deposits	33,938	33,866	34,257
Other
Segment Reporting Information [Line Items]
Net interest income	171	193	53
Non-interest income	(5)	(63)	(39)
Total net revenue	166	130	14
Provision for loan, lease and other losses	4	(5)	(2)
Total non-interest expense	442	309	312
Income from continuing operations before income taxes	(280)	(174)	(296)
Income tax provision (benefit)	1,289	(339)	(350)
Income from continuing operations, net of tax	(1,569)	165	54
Loans held for investment	58	64	88
Total deposits	$ 23,922	$ 20,985	$ 10,762