Loans - Loan Portfolio Composition and Aging Analysis (Detail) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	$ 224,092	$ 222,480
Past due	7,315	8,035
Loans held for investment	$ 244,302	$ 245,586	$ 234,603
Financing Receivable, Recorded Investment, Aging, Percent of Total Loan [Abstract]
Financing Receivable, Percent Current	91.73%	90.59%
Total Delinquent Loans (as percent)	2.99%	3.27%
Total Loans (as percent)	100.00%	100.00%
Loans and Leases Receivable, Deferred Income	$ 664	$ 558
Credit Card Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	97,908	101,394
Past due	3,682	4,156
Loans held for investment	101,590	105,552
Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	59,357	55,190
Past due	3,245	3,408
Loans held for investment	74,973	73,054
Consumer Portfolio Segment [Member] | Auto
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	48,733	44,762
Past due	3,032	3,154
Loans held for investment	51,765	47,916
Consumer Portfolio Segment [Member] | Home loan
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	7,203	6,951
Past due	173	205
Loans held for investment	19,724	21,584
Consumer Portfolio Segment [Member] | Retail banking
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	3,421	3,477
Past due	40	49
Loans held for investment	3,484	3,554
Commercial Banking
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	66,768	65,840
Past due	380	463
Loans held for investment	67,672	66,916
Commercial Banking | Total commercial lending
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	66,334	65,367
Past due	371	453
Loans held for investment	67,229	66,433
Commercial Banking | Commercial and multifamily real estate
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	27,334	26,536
Past due	68	45
Loans held for investment	27,428	26,609
Commercial Banking | Commercial and industrial
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	39,000	38,831
Past due	303	408
Loans held for investment	39,801	39,824
Commercial Banking | Small-ticket commercial real estate
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	434	473
Past due	9	10
Loans held for investment	443	483
Other
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	59	56
Past due	8	8
Loans held for investment	67	64
Receivables Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Loans held for investment	$ 12,895	$ 15,071
Financing Receivable, Recorded Investment, Aging, Percent of Total Loan [Abstract]
Total Loans (as percent)	5.28%	6.14%
Receivables Acquired with Deteriorated Credit Quality [Member] | Credit Card Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Loans held for investment	$ 0	$ 2
Receivables Acquired with Deteriorated Credit Quality [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Loans held for investment	12,371	14,456
Receivables Acquired with Deteriorated Credit Quality [Member] | Consumer Portfolio Segment [Member] | Auto
Financing Receivable, Recorded Investment, Aging [Abstract]
Loans held for investment	0	0
Receivables Acquired with Deteriorated Credit Quality [Member] | Consumer Portfolio Segment [Member] | Home loan
Financing Receivable, Recorded Investment, Aging [Abstract]
Loans held for investment	12,348	14,428
Receivables Acquired with Deteriorated Credit Quality [Member] | Consumer Portfolio Segment [Member] | Retail banking
Financing Receivable, Recorded Investment, Aging [Abstract]
Loans held for investment	23	28
Receivables Acquired with Deteriorated Credit Quality [Member] | Commercial Banking
Financing Receivable, Recorded Investment, Aging [Abstract]
Loans held for investment	524	613
Receivables Acquired with Deteriorated Credit Quality [Member] | Commercial Banking | Total commercial lending
Financing Receivable, Recorded Investment, Aging [Abstract]
Loans held for investment	524	613
Receivables Acquired with Deteriorated Credit Quality [Member] | Commercial Banking | Commercial and multifamily real estate
Financing Receivable, Recorded Investment, Aging [Abstract]
Loans held for investment	26	28
Receivables Acquired with Deteriorated Credit Quality [Member] | Commercial Banking | Commercial and industrial
Financing Receivable, Recorded Investment, Aging [Abstract]
Loans held for investment	498	585
Receivables Acquired with Deteriorated Credit Quality [Member] | Commercial Banking | Small-ticket commercial real estate
Financing Receivable, Recorded Investment, Aging [Abstract]
Loans held for investment	0	0
Receivables Acquired with Deteriorated Credit Quality [Member] | Other
Financing Receivable, Recorded Investment, Aging [Abstract]
Loans held for investment	0	0
Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	$ 3,355	$ 3,466
Financing Receivable, Recorded Investment, Aging, Percent of Total Loan [Abstract]
Total Delinquent Loans (as percent)	1.37%	1.41%
Financing Receivables, 30 to 59 Days Past Due [Member] | Credit Card Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	$ 1,226	$ 1,277
Financing Receivables, 30 to 59 Days Past Due [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	2,034	2,107
Financing Receivables, 30 to 59 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Auto
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	1,984	2,041
Financing Receivables, 30 to 59 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Home loan
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	34	44
Financing Receivables, 30 to 59 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Retail banking
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	16	22
Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial Banking
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	92	79
Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial Banking | Total commercial lending
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	90	72
Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial Banking | Commercial and multifamily real estate
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	39	45
Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial Banking | Commercial and industrial
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	51	27
Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial Banking | Small-ticket commercial real estate
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	2	7
Financing Receivables, 30 to 59 Days Past Due [Member] | Other
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	3	3
Financing Receivables, 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	$ 1,659	$ 1,920
Financing Receivable, Recorded Investment, Aging, Percent of Total Loan [Abstract]
Total Delinquent Loans (as percent)	0.68%	0.78%
Financing Receivables, 60 to 89 Days Past Due [Member] | Credit Card Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	$ 793	$ 918
Financing Receivables, 60 to 89 Days Past Due [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	851	917
Financing Receivables, 60 to 89 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Auto
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	833	890
Financing Receivables, 60 to 89 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Home loan
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	13	20
Financing Receivables, 60 to 89 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Retail banking
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	5	7
Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial Banking
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	15	85
Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial Banking | Total commercial lending
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	14	84
Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial Banking | Commercial and multifamily real estate
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	0	0
Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial Banking | Commercial and industrial
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	14	84
Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial Banking | Small-ticket commercial real estate
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	1	1
Financing Receivables, 60 to 89 Days Past Due [Member] | Other
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	0	0
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	$ 2,301	$ 2,649
Financing Receivable, Recorded Investment, Aging, Percent of Total Loan [Abstract]
Total Delinquent Loans (as percent)	0.94%	1.08%
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Credit Card Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	$ 1,663	$ 1,961
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	360	384
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Auto
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	215	223
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Home loan
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	126	141
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Retail banking
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	19	20
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial Banking
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	273	299
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial Banking | Total commercial lending
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	267	297
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial Banking | Commercial and multifamily real estate
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	29	0
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial Banking | Commercial and industrial
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	238	297
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial Banking | Small-ticket commercial real estate
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	6	2
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Other
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	5	5
Geographic Distribution, Domestic [Member] | Credit Card Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	89,493	93,279
Past due	3,373	3,839
Loans held for investment	92,866	97,120
Geographic Distribution, Domestic [Member] | Receivables Acquired with Deteriorated Credit Quality [Member] | Credit Card Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Loans held for investment	0	2
Geographic Distribution, Domestic [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Credit Card Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	1,105	1,153
Geographic Distribution, Domestic [Member] | Financing Receivables, 60 to 89 Days Past Due [Member] | Credit Card Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	726	846
Geographic Distribution, Domestic [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Credit Card Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	1,542	1,840
Geographic Distribution, Foreign [Member] | Credit Card Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	8,415	8,115
Past due	309	317
Loans held for investment	8,724	8,432
Geographic Distribution, Foreign [Member] | Receivables Acquired with Deteriorated Credit Quality [Member] | Credit Card Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Loans held for investment	0	0
Geographic Distribution, Foreign [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Credit Card Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	121	124
Geographic Distribution, Foreign [Member] | Financing Receivables, 60 to 89 Days Past Due [Member] | Credit Card Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	67	72
Geographic Distribution, Foreign [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Credit Card Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	121	121
Operating Segments [Member] | Consumer Banking
Financing Receivable, Recorded Investment, Aging [Abstract]
Loans held for investment	$ 74,973	$ 66,916	$ 71,415