Loans - Credit Card Loan Portfolio (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	$ 832,792	$ 747,508	$ 724,177
Credit card
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	131,387	128,027	$ 127,465
Credit card loans | Credit card
Loans and Leases Receivable Disclosure [Line Items]
Net charge-offs	$ 3,122	$ 3,429
% of net charge-offs to retained loans	2.51%	2.75%
Total retained loans	$ 131,387	$ 128,027
Total 30 day delinquency rate	1.43%	1.44%
% of 90 days past due to total retained loans	0.72%	0.70%
Percentage of portfolio based on carrying value with estimated refreshed FICO scores, Equal to or greater than 660	84.40%	85.70%
Percentage of portfolio based on carrying value with estimated refreshed FICO scores, Less than 660	15.60%	14.30%
Credit card loans | Credit card | California
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	$ 18,802	$ 17,940
Credit card loans | Credit card | Texas
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	11,847	11,088
Credit card loans | Credit card | New York
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	11,360	10,940
Credit card loans | Credit card | Florida
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	7,806	7,398
Credit card loans | Credit card | Illinois
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	7,655	7,497
Credit card loans | Credit card | New Jersey
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	5,879	5,750
Credit card loans | Credit card | Ohio
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	4,700	4,707
Credit card loans | Credit card | Pennsylvania
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	4,533	4,489
Credit card loans | Credit card | Michigan
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	3,562	3,552
Credit card loans | Credit card | Colorado
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	3,399	3,226
Credit card loans | Credit card | All other
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	$ 51,844	51,440
Credit card loans | Credit card | 30 or more days past due
Loans and Leases Receivable Disclosure [Line Items]
Loans, charge-off criteria, period past due	30 days
Credit card loans | Credit card | 90 or more days past due
Loans and Leases Receivable Disclosure [Line Items]
Loans, charge-off criteria, period past due	90 days
Credit card loans | Credit card | Current and less than 30 days past due and still accruing
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	$ 129,502	126,189
Credit card loans | Credit card | 30–89 days past due and still accruing
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	941	943
Credit card loans | Credit card | 90 or more days past due and still accruing
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	$ 944	$ 895