Loans - Credit Card Portfolio - Impaired Loans (Details) - Credit card - Consumer Credit Card Financing Receivable - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Financing Receivable, Impaired [Line Items]
Loans with modified payment terms	$ 1,480		$ 1,480		$ 1,775
Modified credit card loans that have reverted to pre-modification payment terms	205		205		254
Total impaired loans	1,685		1,685		2,029
Allowance for loan losses related to impaired loans	518		518		500
Average impaired loans	1,769	$ 2,617	1,854	$ 2,776
Interest income on impaired loans	21	$ 32	44	$ 68
Noncompliance with Modified Terms
Financing Receivable, Impaired [Line Items]
Modified credit card loans that have reverted to pre-modification payment terms	127		127		159
Completion of Short Term Modification
Financing Receivable, Impaired [Line Items]
Modified credit card loans that have reverted to pre-modification payment terms	$ 78		$ 78		$ 95