Loans - Credit Card Loan Portfolio (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	$ 756,971,000,000	$ 747,508,000,000	$ 721,160,000,000
Credit card
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	120,835,000,000	128,027,000,000	121,512,000,000
Credit card | Consumer Credit Card Financing Receivable
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	120,835,000,000	128,027,000,000
% of 30 days past due to total retained loans	1.41%	1.44%
% of 90 days past due to total retained loans	0.73%	0.70%
Percentage of Loans with FICO Scores of 660 Or Greater to Total Retained Loans	85.20%	85.70%
Percentage of Loans with FICO Scores Less than 660 to Total Retained Loans	14.80%	14.30%
Credit card | Consumer Credit Card Financing Receivable | California
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	17,133,000,000	17,940,000,000
Credit card | Consumer Credit Card Financing Receivable | Texas
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	10,605,000,000	11,088,000,000
Credit card | Consumer Credit Card Financing Receivable | New York
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	10,414,000,000	10,940,000,000
Credit card | Consumer Credit Card Financing Receivable | Illinois
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	7,058,000,000	7,497,000,000
Credit card | Consumer Credit Card Financing Receivable | Florida
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	7,126,000,000	7,398,000,000
Credit card | Consumer Credit Card Financing Receivable | New Jersey
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	5,427,000,000	5,750,000,000
Credit card | Consumer Credit Card Financing Receivable | Ohio
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	4,389,000,000	4,707,000,000
Credit card | Consumer Credit Card Financing Receivable | Pennsylvania
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	4,197,000,000	4,489,000,000
Credit card | Consumer Credit Card Financing Receivable | Michigan
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	3,340,000,000	3,552,000,000
Credit card | Consumer Credit Card Financing Receivable | Virginia
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	2,958,000,000	3,263,000,000
Credit card | Consumer Credit Card Financing Receivable | All other
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	48,188,000,000	51,403,000,000
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	119,132,000,000	126,189,000,000
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	826,000,000	943,000,000
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	877,000,000	895,000,000
Credit card | Consumer Credit Card Financing Receivable | Nonaccrual
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	$ 0	$ 0