Debt (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Long-term debt and other financing obligations [Abstract]
Other financing obligations	$ 170	$ 172
Total long-term debt and other financing obligations	645	647
Less: Current portion of debt	5	5
Total long-term debt and other financing obligations, less current maturities	640	642
Senior Notes, 5.95%, due 2015 [Member]
Long-term debt and other financing obligations [Abstract]
Total long-term debt	35	35
Interest rate on notes issued	5.95%	5.95%
Senior Notes, 6.80%, due 2015 [Member]
Long-term debt and other financing obligations [Abstract]
Total long-term debt	340	340
Interest rate on notes issued	6.80%	6.80%
Senior Debentures, 6.85%, due 2037 [Member]
Long-term debt and other financing obligations [Abstract]
Total long-term debt	$ 100	$ 100
Interest rate on notes issued	6.85%	6.85%