Fair Value of Financial Instruments (Schedule of Estimated Fair Value of Financial Instruments, by Balance Sheet Grouping) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Assets:
Available-for-sale securities	$ 245	$ 65
Trading securities	42	38
Liabilities:
Contingent Value Right, Fair Value Disclosure	16
Carrying Amount Measurement [Member]
Assets:
Cash and cash equivalents	613	373
Available-for-sale securities	245	65
Trading securities	42	38
Liabilities:
Contingent Value Right, Fair Value Disclosure	16
Carrying Amount Measurement [Member] | Credit Facility, Type of Debt [Member] | Credit Facility, Name [Member]
Liabilities:
Credit Facility, Fair Value Disclosure	7,262	4,050
Carrying Amount Measurement [Member] | Senior Notes [Member] | Senior Notes at 8.0, Due 2019 [Member]
Liabilities:
Notes Payable, Fair Value Disclosure	2,020	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	702	537
Estimate of Fair Value Measurement [Member]
Assets:
Cash and cash equivalents	613	373
Available-for-sale securities	245	65
Trading securities	42	38
Liabilities:
Contingent Value Right, Fair Value Disclosure	16
Estimate of Fair Value Measurement [Member] | Credit Facility, Type of Debt [Member] | Credit Facility, Name [Member]
Liabilities:
Credit Facility, Fair Value Disclosure	7,315	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	2,206	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	3,144
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	1,689	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	1,028
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	$ 702	$ 537