Loans - Credit Card Loan Portfolio (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans retained	$ 735,304	$ 724,177	$ 722,471
Credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans retained	126,564	127,465	123,672
Credit card | Credit Card Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans retained	126,564	127,465
Percentage of loans 30 plus days past due to total retained loans	1.43%	1.67%
Percentage of loans 90 plus days past due to total retained loans	0.67%	0.80%
Percentage of Loans with FICO Scores of 660 Or Greater to Total Retained Loans	83.80%	85.10%
Percentage of Loans with FICO Scores Less than 660 to Total Retained Loans	16.20%	14.90%
Credit card | Credit Card Loan | California
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans retained	17,238	17,194
Credit card | Credit Card Loan | Texas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans retained	10,648	10,400
Credit card | Credit Card Loan | New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans retained	10,642	10,497
Credit card | Credit Card Loan | Illinois
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans retained	7,390	7,412
Credit card | Credit Card Loan | Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans retained	7,140	7,178
Credit card | Credit Card Loan | New Jersey
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans retained	5,575	5,554
Credit card | Credit Card Loan | Ohio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans retained	4,732	4,881
Credit card | Credit Card Loan | Pennsylvania
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans retained	4,359	4,462
Credit card | Credit Card Loan | Michigan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans retained	3,524	3,618
Credit card | Credit Card Loan | Virginia
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans retained	3,183	3,239
Credit card | Credit Card Loan | All other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans retained	52,133	53,030
Credit card | Credit Card Loan | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans retained	124,752	125,335
Credit card | Credit Card Loan | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans retained	962	1,108
Credit card | Credit Card Loan | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans retained	850	1,022
Credit card | Credit Card Loan | Nonaccrual loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans retained	$ 0	$ 0