Fair Value Measurements (Financial Instruments) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Level 1 [Member] | Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Subordinated convertible debentures	$ 55		$ 55
Senior and senior subordinated notes	5,387		1,732
Level 1 [Member] | Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Subordinated convertible debentures	63		49
Senior and senior subordinated notes	5,881		1,795
Level 2 [Member] | Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
4 percent Convertible Senior Notes (1)	137	[1]	129	[1]
Level 2 [Member] | Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
4 percent Convertible Senior Notes (1)	155	[1]	138	[1]
Level 3 [Member] | Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Capital leases (2)	148	[2]	39	[2]
Level 3 [Member] | Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Capital leases (2)	$ 145	[2]	$ 33	[2]

[1] The fair value of the 4 percent Convertible Senior Notes is based on the market value of comparable notes. Consistent with the carrying amount, the fair value excludes the equity component of the notes. To exclude the equity component and calculate the fair value, we used an effective interest rate of 6.9 percent.

[2] The fair value of capital leases reflects the present value of the leases using a 7.0 percent interest rate.