Loans - Credit Card: Risk Profile by Geographic Region and Delinquency Status (Detail) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 240,588	$ 245,586	$ 227,613
Credit Card Portfolio Segment [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 99,213	$ 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	$ 10,480	$ 11,068
Percentage of portfolio	10.60%	10.50%
Credit Card Portfolio Segment [Member] | Texas
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 6,875	$ 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	$ 6,623	$ 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	$ 6,191	$ 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	$ 4,178	$ 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	$ 3,747	$ 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	$ 3,368	$ 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	$ 3,246	$ 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	$ 2,924	$ 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	$ 43,460	$ 46,349
Percentage of portfolio	43.80%	43.90%
Credit Card Portfolio Segment [Member] | Canada
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 5,283	$ 5,594
Percentage of portfolio	5.30%	5.30%
Credit Card Portfolio Segment [Member] | United Kingdom
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 2,838	$ 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]
Loans held for investment	$ 91,092	$ 97,120
Percentage of portfolio	91.80%	92.00%
Credit Card Portfolio Segment [Member] | Geographic Distribution, Foreign [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 8,121	$ 8,432
Percentage of portfolio	8.20%	8.00%