Debt and Borrowing Arrangements (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Debt and Borrowing Arrangements
Total Debt	$ 6,323	$ 6,554
Vehicle Management Asset-Backed Debt
Debt and Borrowing Arrangements
Total Debt	3,535	3,457
Term notes, in amortization
Debt and Borrowing Arrangements
Total Debt	827	424
Weighted Avg-Interest Rate (as a percent)	1.30%	2.20%
Term notes, in revolving period
Debt and Borrowing Arrangements
Total Debt	1,650	1,593
Weighted Avg-Interest Rate (as a percent)	0.90%	1.00%
Variable-funding notes
Debt and Borrowing Arrangements
Total Debt	1,036	1,415
Weighted Avg-Interest Rate (as a percent)	2.10%	1.60%
Other
Debt and Borrowing Arrangements
Total Debt	22	25
Weighted Avg-Interest Rate (as a percent)	5.00%	5.10%
Mortgage Asset-Backed Debt
Debt and Borrowing Arrangements
Total Debt	1,617	1,941
Committed warehouse facilities
Debt and Borrowing Arrangements
Total Debt	1,552	1,875
Weighted Avg-Interest Rate (as a percent)	2.10%	2.00%
Servicing advance facility
Debt and Borrowing Arrangements
Total Debt	65	66
Weighted Avg-Interest Rate (as a percent)	2.70%	2.70%
Unsecured Debt
Debt and Borrowing Arrangements
Total Debt	1,171	1,156
Term notes
Debt and Borrowing Arrangements
Total Debt	732	732
Weighted Avg-Interest Rate (as a percent)	8.50%	8.50%
Convertible notes
Debt and Borrowing Arrangements
Total Debt	439	424
Weighted Avg-Interest Rate (as a percent)	5.00%	5.00%
Unamortized discount	$ 61	$ 76
Effective interest rate (as a percent)	13.00%	13.00%