Receivables Receivables - Retrospective Review of Trouble Debt Restructuring (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
New TDR Loan Volume Upon Adoption of New Accounting Standards Update [Abstract]
Interest rate modification	$ 173	$ 497	$ 392	$ 1,225
Re-age of past due account	362	445	718	1,240
Total	$ 535	$ 942	$ 1,110	$ 2,465