Loans - Loan Portfolio Composition and Aging Analysis (Detail) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	$ 219,451	$ 222,480
Past due	7,035	8,035
Loans held for investment	$ 240,588	$ 245,586	$ 227,613
Financing Receivable, Recorded Investment, Aging, Percent of Total Loan [Abstract]
Financing Receivable, Percent Current	91.21%	90.59%
Total Delinquent Loans (as percent)	2.92%	3.27%
Total Loans (as percent)	100.00%	100.00%
Loans and Leases Receivable, Deferred Income	$ 598	$ 558
Credit Card Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	95,532	101,394
Past due	3,681	4,156
Loans held for investment	99,213	105,552
Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	57,570	55,190
Past due	2,904	3,408
Loans held for investment	73,982	73,054
Consumer Portfolio Segment [Member] | Auto
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	47,092	44,762
Past due	2,679	3,154
Loans held for investment	49,771	47,916
Consumer Portfolio Segment [Member] | Home loan
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	7,069	6,951
Past due	185	205
Loans held for investment	20,738	21,584
Consumer Portfolio Segment [Member] | Retail banking
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	3,409	3,477
Past due	40	49
Loans held for investment	3,473	3,554
Commercial Banking
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	66,285	65,840
Past due	441	463
Loans held for investment	67,320	66,916
Commercial Banking | Total commercial lending
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	65,829	65,367
Past due	433	453
Loans held for investment	66,856	66,433
Commercial Banking | Commercial and multifamily real estate
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	27,152	26,536
Past due	35	45
Loans held for investment	27,218	26,609
Commercial Banking | Commercial and industrial
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	38,677	38,831
Past due	398	408
Loans held for investment	39,638	39,824
Commercial Banking | Small-ticket commercial real estate
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	456	473
Past due	8	10
Loans held for investment	464	483
Other
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	64	56
Past due	9	8
Loans held for investment	73	64
Receivables Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Loans held for investment	$ 14,102	$ 15,071
Financing Receivable, Recorded Investment, Aging, Percent of Total Loan [Abstract]
Total Loans (as percent)	5.87%	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	13,508	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	13,484	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	24	28
Receivables Acquired with Deteriorated Credit Quality [Member] | Commercial Banking
Financing Receivable, Recorded Investment, Aging [Abstract]
Loans held for investment	594	613
Receivables Acquired with Deteriorated Credit Quality [Member] | Commercial Banking | Total commercial lending
Financing Receivable, Recorded Investment, Aging [Abstract]
Loans held for investment	594	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	31	28
Receivables Acquired with Deteriorated Credit Quality [Member] | Commercial Banking | Commercial and industrial
Financing Receivable, Recorded Investment, Aging [Abstract]
Loans held for investment	563	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	$ 3,036	$ 3,466
Financing Receivable, Recorded Investment, Aging, Percent of Total Loan [Abstract]
Total Delinquent Loans (as percent)	1.26%	1.41%
Financing Receivables, 30 to 59 Days Past Due [Member] | Credit Card Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	$ 1,059	$ 1,277
Financing Receivables, 30 to 59 Days Past Due [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	1,894	2,107
Financing Receivables, 30 to 59 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Auto
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	1,846	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	33	44
Financing Receivables, 30 to 59 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Retail banking
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	15	22
Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial Banking
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	80	79
Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial Banking | Total commercial lending
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	79	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	9	45
Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial Banking | Commercial and industrial
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	70	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	1	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	$ 1,484	$ 1,920
Financing Receivable, Recorded Investment, Aging, Percent of Total Loan [Abstract]
Total Delinquent Loans (as percent)	0.62%	0.78%
Financing Receivables, 60 to 89 Days Past Due [Member] | Credit Card Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	$ 781	$ 918
Financing Receivables, 60 to 89 Days Past Due [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	686	917
Financing Receivables, 60 to 89 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Auto
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	662	890
Financing Receivables, 60 to 89 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Home loan
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	16	20
Financing Receivables, 60 to 89 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Retail banking
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	8	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	2	0
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	$ 2,515	$ 2,649
Financing Receivable, Recorded Investment, Aging, Percent of Total Loan [Abstract]
Total Delinquent Loans (as percent)	1.04%	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	$ 1,841	$ 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	324	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	171	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	136	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	17	20
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial Banking
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due	346	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	340	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	26	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	314	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	4	5
Geographic Distribution, Domestic [Member] | Credit Card Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	87,716	93,279
Past due	3,376	3,839
Loans held for investment	91,092	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	945	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	711	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	1,720	1,840
Geographic Distribution, Foreign [Member] | Credit Card Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	7,816	8,115
Past due	305	317
Loans held for investment	8,121	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	114	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	70	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