Fair Value of Financial Instruments (Schedule of Estimated Fair Value of Financial Instruments, by Balance Sheet Grouping) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Assets:
Available-for-sale securities	$ 264	$ 65
Trading securities	52	38
Liabilities:
Contingent Value Right, Fair Value Disclosure	18
Carrying Amount Measurement [Member]
Assets:
Cash and cash equivalents	389	373
Available-for-sale securities	264	65
Trading securities	52	38
Liabilities:
Contingent Value Right, Fair Value Disclosure	18
Carrying Amount Measurement [Member] | Credit Facility, Type of Debt [Member] | Credit Facility, Name [Member]
Liabilities:
Credit Facility, Fair Value Disclosure	7,229	4,050
Carrying Amount Measurement [Member] | Senior Notes [Member] | Senior Notes at 8.0, Due 2019 [Member]
Liabilities:
Notes Payable, Fair Value Disclosure	2,019	2,020
Carrying Amount Measurement [Member] | Senior Notes [Member] | Senior Notes at 7.125, Due 2020 [Member]
Liabilities:
Notes Payable, Fair Value Disclosure	1,200	1,200
Carrying Amount Measurement [Member] | Senior Notes [Member] | Senior Notes at 6.875, Due 2022 [Member]
Liabilities:
Notes Payable, Fair Value Disclosure	3,000
Carrying Amount Measurement [Member] | Senior Secured Notes [Member] | Senior Secured Notes At 5.125 Due 2018 [Member]
Liabilities:
Notes Payable, Fair Value Disclosure	1,600	1,600
Carrying Amount Measurement [Member] | Senior Secured Notes [Member] | Senior Secured Notes at 5.125, Due 2021 [Member]
Liabilities:
Notes Payable, Fair Value Disclosure	1,000
Carrying Amount Measurement [Member] | Receivables Facility and Other Debt, Type [Member] | Receivables Facility and Unsecured Debt [Member]
Liabilities:
Other Liabilities, Fair Value Disclosure	674	537
Estimate of Fair Value Measurement [Member]
Assets:
Cash and cash equivalents	389	373
Available-for-sale securities	264	65
Trading securities	52	38
Liabilities:
Contingent Value Right, Fair Value Disclosure	18
Estimate of Fair Value Measurement [Member] | Credit Facility, Type of Debt [Member] | Credit Facility, Name [Member]
Liabilities:
Credit Facility, Fair Value Disclosure	7,270	4,085
Estimate of Fair Value Measurement [Member] | Senior Notes [Member] | Senior Notes at 8.0, Due 2019 [Member]
Liabilities:
Notes Payable, Fair Value Disclosure	2,198	2,172
Estimate of Fair Value Measurement [Member] | Senior Notes [Member] | Senior Notes at 7.125, Due 2020 [Member]
Liabilities:
Notes Payable, Fair Value Disclosure	1,306	1,246
Estimate of Fair Value Measurement [Member] | Senior Notes [Member] | Senior Notes at 6.875, Due 2022 [Member]
Liabilities:
Notes Payable, Fair Value Disclosure	3,180
Estimate of Fair Value Measurement [Member] | Senior Secured Notes [Member] | Senior Secured Notes At 5.125 Due 2018 [Member]
Liabilities:
Notes Payable, Fair Value Disclosure	1,680	1,662
Estimate of Fair Value Measurement [Member] | Senior Secured Notes [Member] | Senior Secured Notes at 5.125, Due 2021 [Member]
Liabilities:
Notes Payable, Fair Value Disclosure	1,029
Estimate of Fair Value Measurement [Member] | Receivables Facility and Other Debt, Type [Member] | Receivables Facility and Unsecured Debt [Member]
Liabilities:
Other Liabilities, Fair Value Disclosure	$ 674	$ 537