Long-Term Debt (Schedule of Debt) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Less: Unamortized deferred debt issuance costs and note premium	$ (169)	$ (193)
Debt	13,913	15,244
Less: Current maturities	(33)	(455)
Long-term debt	13,880	14,789
Secured Debt [Member] | Credit Facility, Term Loan A [Member]
Debt Instrument [Line Items]
Debt		749
Secured Debt [Member] | Credit Facility, Term Loan F [Member]
Debt Instrument [Line Items]
Debt		1,445
Secured Debt [Member] | Credit Facility, Term Loan G [Member]
Debt Instrument [Line Items]
Debt	1,037	1,528
Secured Debt [Member] | Credit Facility, Term Loan H [Member]
Debt Instrument [Line Items]
Debt	1,903	2,811
Senior Notes [Member] | Senior Notes at 8.0, Due 2019 [Member]
Debt Instrument [Line Items]
Debt	1,925	1,925
Senior Notes [Member] | Senior Notes at 7.125, Due 2020 [Member]
Debt Instrument [Line Items]
Debt	1,200	1,200
Senior Notes [Member] | Senior Notes at 6.875, Due 2022 [Member]
Debt Instrument [Line Items]
Debt	3,000	3,000
Senior Secured Notes [Member] | Senior Secured Notes At 5.125 Due 2018 [Member]
Debt Instrument [Line Items]
Debt		700
Senior Secured Notes [Member] | Senior Secured Notes at 5.125, Due 2021 [Member]
Debt Instrument [Line Items]
Debt	1,000	1,000
Senior Secured Notes [Member] | Senior Secured Notes at 6.25, Due 2023 [Member]
Debt Instrument [Line Items]
Debt	3,100
Receivables Facility [Member] | Receivables Facility, Name [Member]
Debt Instrument [Line Items]
Debt	565	677
Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Debt	304	328
Unsecured Debt [Member]
Debt Instrument [Line Items]
Debt	$ 48	$ 74