Allowance for Loan and Lease Losses - Components of Allowance for Loan and Lease Losses by Impairment Methodology (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015
Allowance for loan and lease losses by impairment methodology:
Collectively evaluated	$ 6,948		$ 6,007
Asset-specific	432		465
Total allowance for loan and lease losses	7,418		6,503
Loans held for investment by impairment methodology:
Collectively evaluated	237,665		227,555
Asset-specific	2,772		2,960
Loans held for investment	$ 252,422		$ 245,586	$ 238,019
Allowance as a percentage of period-end loans held for investment	2.94%		2.65%
Credit Card Portfolio Segment [Member]
Allowance for loan and lease losses by impairment methodology:
Collectively evaluated	$ 5,246		$ 4,367
Asset-specific	288		239
Total allowance for loan and lease losses	5,534	$ 5,210	4,606	4,445	$ 4,086	$ 3,654
Loans held for investment by impairment methodology:
Collectively evaluated	108,322		104,835
Asset-specific	777		715
Loans held for investment	$ 109,130		$ 105,552
Allowance as a percentage of period-end loans held for investment	5.07%		4.36%
Consumer Portfolio Segment [Member]
Allowance for loan and lease losses by impairment methodology:
Collectively evaluated	$ 1,125		$ 1,016
Asset-specific	55		57
Total allowance for loan and lease losses	1,213	1,199	1,102	1,003	972	868
Loans held for investment by impairment methodology:
Collectively evaluated	63,432		57,862
Asset-specific	681		736
Loans held for investment	$ 75,564		$ 73,054
Allowance as a percentage of period-end loans held for investment	1.61%		1.51%
Commercial Banking
Allowance for loan and lease losses by impairment methodology:
Collectively evaluated	$ 575		$ 622
Asset-specific	89		169
Total allowance for loan and lease losses	669	758	793	808	821	604
Loans held for investment by impairment methodology:
Collectively evaluated	65,853		64,794
Asset-specific	1,314		1,509
Loans held for investment	$ 67,670		$ 66,916
Allowance as a percentage of period-end loans held for investment	0.99%		1.19%
Other
Allowance for loan and lease losses by impairment methodology:
Collectively evaluated	$ 2		$ 2
Asset-specific	0		0
Total allowance for loan and lease losses	2	$ 3	2	$ 2	$ 2	$ 4
Loans held for investment by impairment methodology:
Collectively evaluated	58		64
Asset-specific	0		0
Loans held for investment	$ 58		$ 64
Allowance as a percentage of period-end loans held for investment	3.45%		3.13%
Receivables Acquired with Deteriorated Credit Quality [Member]
Allowance for loan and lease losses by impairment methodology:
Financing Receivable, Allowance for Credit Losses	$ 38		$ 31
Loans held for investment by impairment methodology:
Loans held for investment	11,985		15,071
Receivables Acquired with Deteriorated Credit Quality [Member] | Credit Card Portfolio Segment [Member]
Allowance for loan and lease losses by impairment methodology:
Financing Receivable, Allowance for Credit Losses	0		0
Loans held for investment by impairment methodology:
Loans held for investment	31		2
Receivables Acquired with Deteriorated Credit Quality [Member] | Consumer Portfolio Segment [Member]
Allowance for loan and lease losses by impairment methodology:
Financing Receivable, Allowance for Credit Losses	33		29
Loans held for investment by impairment methodology:
Loans held for investment	11,451		14,456
Receivables Acquired with Deteriorated Credit Quality [Member] | Commercial Banking
Allowance for loan and lease losses by impairment methodology:
Financing Receivable, Allowance for Credit Losses	5		2
Loans held for investment by impairment methodology:
Loans held for investment	503		613
Receivables Acquired with Deteriorated Credit Quality [Member] | Other
Allowance for loan and lease losses by impairment methodology:
Financing Receivable, Allowance for Credit Losses	0		0
Loans held for investment by impairment methodology:
Loans held for investment	$ 0		$ 0