Loans Loans - Credit Card Portfolio - Loan Modifications (Details) (Credit card, Consumer Credit Card Financing Receivable, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 payment	Dec. 31, 2013	Dec. 31, 2012
Financing Receivable, Impaired [Line Items]
Fixed payment plan period	60 months
Weighted-average interest rate of loans – before TDR	14.96%	15.37%	15.67%
Weighted-average interest rate of loans – after TDR	4.40%	4.38%	5.19%
Modifications, subsequent default, recorded investment	$ 119	$ 167	$ 309
Number of years before payment default under a modified loan	1 year
Number of payments past due for deemed payment	2
Rate of default for modified loans, estimated weighted average	27.91%	30.72%	38.23%
Total new enrollments
Financing Receivable, Impaired [Line Items]
New TDRs	$ 807	$ 1,200	$ 1,700