Loans - Net Gains and Losses on Sale (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Loans and Leases Receivable Disclosure [Line Items]
Total net gains/(losses) on sales of loans (including lower of cost or fair value adjustments)	$ 201	$ 240	$ 293
Consumer, excluding credit card
Loans and Leases Receivable Disclosure [Line Items]
Total net gains/(losses) on sales of loans (including lower of cost or fair value adjustments)	341	313	122
Credit card
Loans and Leases Receivable Disclosure [Line Items]
Total net gains/(losses) on sales of loans (including lower of cost or fair value adjustments)	(241)	3	(9)
Wholesale
Loans and Leases Receivable Disclosure [Line Items]
Total net gains/(losses) on sales of loans (including lower of cost or fair value adjustments)	$ 101	$ (76)	$ 180