Long-Term Debt (Schedule of Maturities of Long-Term Debt) (Details) $ in Millions	Dec. 31, 2017 USD ($)
Long-term Debt, Fiscal Year Maturity
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 33
Long-term Debt, Maturities, Repayments of Principal in Year Two	3,569
Long-term Debt, Maturities, Repayments of Principal in Year Three	1,210
Long-term Debt, Maturities, Repayments of Principal in Year Four	2,913
Long-term Debt, Maturities, Repayments of Principal in Year Five	3,010
Long-term Debt, Maturities, Repayments of Principal after Year Five	3,347
Total maturities	14,082
Less: Deferred debt issuance costs	(191)
Plus unamortized note premium	22
Long-term Debt, Total	13,913
Term Loans [Member]
Long-term Debt, Fiscal Year Maturity
Long-term Debt, Maturities, Repayments of Principal in Year Two	1,037
Long-term Debt, Maturities, Repayments of Principal in Year Four	1,903
Total maturities	2,940
Less: Deferred debt issuance costs	(38)
Long-term Debt, Total	$ 2,902