Loans - Credit Card: Risk Profile by Geographic Region and Delinquency Status (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 254,473	$ 245,586	$ 229,851
Credit Card Portfolio Segment [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 114,762	$ 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	$ 11,475	$ 11,068
Percentage of portfolio	10.00%	10.50%
Credit Card Portfolio Segment [Member] | Texas
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 7,847	$ 7,227
Percentage of portfolio	6.80%	6.80%
Credit Card Portfolio Segment [Member] | New York
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 7,389	$ 7,090
Percentage of portfolio	6.40%	6.70%
Credit Card Portfolio Segment [Member] | Florida
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 6,790	$ 6,540
Percentage of portfolio	5.90%	6.20%
Credit Card Portfolio Segment [Member] | Illinois
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 4,734	$ 4,492
Percentage of portfolio	4.10%	4.30%
Credit Card Portfolio Segment [Member] | Pennsylvania
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 4,550	$ 4,048
Percentage of portfolio	4.00%	3.80%
Credit Card Portfolio Segment [Member] | Ohio
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 3,929	$ 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	$ 3,621	$ 3,488
Percentage of portfolio	3.20%	3.30%
Credit Card Portfolio Segment [Member] | Michigan
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 3,523	$ 3,164
Percentage of portfolio	3.10%	3.00%
Credit Card Portfolio Segment [Member] | Other
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 51,435	$ 46,349
Percentage of portfolio	44.80%	43.90%
Credit Card Portfolio Segment [Member] | Canada
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 6,286	$ 5,594
Percentage of portfolio	5.50%	5.30%
Credit Card Portfolio Segment [Member] | United Kingdom
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 3,183	$ 2,838
Percentage of portfolio	2.80%	2.70%
Credit Card Portfolio Segment [Member] | Geographic Distribution, Domestic [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 105,293	$ 97,120
Percentage of portfolio	91.70%	92.00%
Credit Card Portfolio Segment [Member] | Geographic Distribution, Foreign [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 9,469	$ 8,432
Percentage of portfolio	8.30%	8.00%