Loans - Credit Card Portfolio - Impaired Loans (Details) (Credit card, Consumer Credit Card Financing Receivable, USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Financing Receivable, Impaired [Line Items]
Loans with modified payment terms	$ 1,627		$ 1,775
Modified credit card loans that have reverted to pre-modification payment terms	225		254
Total impaired loans	1,852		2,029
Allowance for loan losses related to impaired loans	458		500
Average impaired loans	1,940	2,938
Interest income on impaired loans	23	36
Noncompliance with Modified Terms
Financing Receivable, Impaired [Line Items]
Modified credit card loans that have reverted to pre-modification payment terms	139		159
Completion of Short Term Modification
Financing Receivable, Impaired [Line Items]
Modified credit card loans that have reverted to pre-modification payment terms	$ 86		$ 95