Loans - Credit Card Loan Portfolio (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	$ 779,705	$ 747,508	$ 735,369
Credit card
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	124,705	128,027	$ 125,621
Credit card | Consumer Credit Card Financing Receivable
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	$ 124,705	$ 128,027
% of 30 days past due to total retained loans	1.29%	1.44%
% of 90 days past due to total retained loans	0.63%	0.70%
Percentage of Loans with FICO Scores of 660 Or Greater to Total Retained Loans	85.70%	85.70%
Percentage of Loans with FICO Scores Less than 660 to Total Retained Loans	14.30%	14.30%
Credit card | Consumer Credit Card Financing Receivable | California
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	$ 17,661	$ 17,940
Credit card | Consumer Credit Card Financing Receivable | Texas
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	11,065	11,088
Credit card | Consumer Credit Card Financing Receivable | New York
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	10,763	10,940
Credit card | Consumer Credit Card Financing Receivable | Illinois
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	7,314	7,497
Credit card | Consumer Credit Card Financing Receivable | Florida
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	7,265	7,398
Credit card | Consumer Credit Card Financing Receivable | New Jersey
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	5,632	5,750
Credit card | Consumer Credit Card Financing Receivable | Ohio
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	4,520	4,707
Credit card | Consumer Credit Card Financing Receivable | Pennsylvania
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	4,317	4,489
Credit card | Consumer Credit Card Financing Receivable | Michigan
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	3,418	3,552
Credit card | Consumer Credit Card Financing Receivable | Virginia
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	3,075	3,263
Credit card | Consumer Credit Card Financing Receivable | All other
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	49,675	51,403
Credit card | Consumer Credit Card Financing Receivable | Current and less than 30 days past due and still accruing
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	123,102	126,189
Credit card | Consumer Credit Card Financing Receivable | 30–89 days past due and still accruing
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	812	943
Credit card | Consumer Credit Card Financing Receivable | 90 or more days past due and still accruing
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	791	895
Credit card | Consumer Credit Card Financing Receivable | Nonaccrual
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	$ 0	$ 0