Loans - Credit Card: Risk Profile by Geographic Region and Delinquency Status (Detail) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Percent Past Due	2.99%	3.27%
Financing Receivable, Recorded Investment, Past Due	$ 7,315	$ 8,035
Loans held for investment	244,302	245,586	$ 234,603
Credit Card Portfolio Segment [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Recorded Investment, Past Due	3,682	4,156
Loans held for investment	$ 101,590	$ 105,552
Percentage of portfolio	100.00%	100.00%
Credit Card Portfolio Segment [Member] | California
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 10,629	$ 11,068
Percentage of portfolio	10.40%	10.50%
Credit Card Portfolio Segment [Member] | Texas
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 6,980	$ 7,227
Percentage of portfolio	6.90%	6.80%
Credit Card Portfolio Segment [Member] | New York
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 6,780	$ 7,090
Percentage of portfolio	6.70%	6.70%
Credit Card Portfolio Segment [Member] | Florida
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 6,269	$ 6,540
Percentage of portfolio	6.20%	6.20%
Credit Card Portfolio Segment [Member] | Illinois
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 4,271	$ 4,492
Percentage of portfolio	4.20%	4.30%
Credit Card Portfolio Segment [Member] | Pennsylvania
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 3,822	$ 4,048
Percentage of portfolio	3.80%	3.80%
Credit Card Portfolio Segment [Member] | Ohio
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 3,436	$ 3,654
Percentage of portfolio	3.40%	3.50%
Credit Card Portfolio Segment [Member] | New Jersey
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 3,313	$ 3,488
Percentage of portfolio	3.30%	3.30%
Credit Card Portfolio Segment [Member] | Michigan
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 2,994	$ 3,164
Percentage of portfolio	2.90%	3.00%
Credit Card Portfolio Segment [Member] | Other
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 44,372	$ 46,349
Percentage of portfolio	43.60%	43.90%
Credit Card Portfolio Segment [Member] | Canada
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 5,750	$ 5,594
Percentage of portfolio	5.70%	5.30%
Credit Card Portfolio Segment [Member] | United Kingdom
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 2,974	$ 2,838
Percentage of portfolio	2.90%	2.70%
Credit Card Portfolio Segment [Member] | Geographic Distribution, Domestic [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Recorded Investment, Past Due	$ 3,373	$ 3,839
Loans held for investment	$ 92,866	$ 97,120
Percentage of portfolio	91.40%	92.00%
Credit Card Portfolio Segment [Member] | Geographic Distribution, Foreign [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Recorded Investment, Past Due	$ 309	$ 317
Loans held for investment	$ 8,724	$ 8,432
Percentage of portfolio	8.60%	8.00%