Fair Value Measurements (Fair value of financial instruments) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014		Dec. 31, 2013
Level 2:
Stated interest rate	4.00%
Level 1 | Carrying Amount
Level 1:
Senior and senior subordinated notes	$ 6,066		$ 5,381
Level 1 | Fair Value
Level 1:
Senior and senior subordinated notes	6,527		5,848
Level 2 | Carrying Amount
Level 2:
4 percent Convertible Senior Notes	87	[1]	136	[1]
Level 2 | Fair Value
Level 2:
4 percent Convertible Senior Notes	93	[1]	149	[1]
Convertible subordinated notes—4 percent
Level 2:
Stated interest rate	4.00%
Effective interest rate	6.60%
Debt instrument, convertible if converted value	$ 911

[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 6.6 percent. As discussed below (see Item 3- Quantitative and Qualitative Disclosures about Market Risk), the total cost to settle the notes based on the closing price of our common stock on June 30, 2014 would be $911.