Debt and Borrowing Arrangements (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Debt and Borrowing Arrangements
Total Debt	$ 6,216	$ 6,914
Vehicle Management Asset-Backed Debt
Debt and Borrowing Arrangements
Total Debt	3,251	3,118
Term notes, in amortization
Debt and Borrowing Arrangements
Total Debt	969	1,196
Weighted Avg-Interest Rate (as a percent)	2.10%	2.10%
Term notes, in revolving period
Debt and Borrowing Arrangements
Total Debt	389	374
Weighted Avg-Interest Rate (as a percent)	1.60%	1.60%
Variable-funding notes
Debt and Borrowing Arrangements
Total Debt	1,862	1,516
Weighted Avg-Interest Rate (as a percent)	1.40%	1.40%
Other
Debt and Borrowing Arrangements
Total Debt	31	32
Weighted Avg-Interest Rate (as a percent)	5.10%	5.10%
Mortgage Asset-Backed Debt
Debt and Borrowing Arrangements
Total Debt	1,484	2,436
Committed warehouse facilities
Debt and Borrowing Arrangements
Total Debt	1,405	2,313
Weighted Avg-Interest Rate (as a percent)	2.10%	2.00%
Uncommitted warehouse facilities
Debt and Borrowing Arrangements
Total Debt		44
Weighted Avg-Interest Rate (as a percent)		1.20%
Servicing advance facility
Debt and Borrowing Arrangements
Total Debt	79	79
Weighted Avg-Interest Rate (as a percent)	2.70%	2.80%
Unsecured Debt
Debt and Borrowing Arrangements
Total Debt	1,481	1,339
Term notes
Debt and Borrowing Arrangements
Total Debt	879	879
Weighted Avg-Interest Rate (as a percent)	8.20%	8.20%
Convertible notes
Debt and Borrowing Arrangements
Total Debt	602	460
Weighted Avg-Interest Rate (as a percent)	4.60%	4.00%
Mortgage loan securitization debt certificates
Debt and Borrowing Arrangements
Total Debt		$ 21
Weighted Avg-Interest Rate (as a percent)		7.00%