Fair Value Measurements (Carrying Amount and Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Millions		6 Months Ended		12 Months Ended
	Apr. 26, 2018	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments, net		$ 21		$ 76
Repayments of long-term debt		1,191	$ 287
Carrying Amount [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents		37		916
Derivative instruments, net		21		76
Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents		37		916
Derivative instruments, net		$ 21		$ 76
Long-term Debt [Member] | 2016 Term Loan due December 2020 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maturity date, year and month				2020-12
Repayments of long-term debt	$ 1,191
Long-term Debt [Member] | 2018 Term Loan due December 2020 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maturity date, year and month		2020-12
Long-term Debt [Member] | Carrying Amount [Member] | 2018 Term Loan due December 2020 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans				$ 1,191
Long-term Debt [Member] | Fair Value [Member] | 2018 Term Loan due December 2020 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans				1,191
Senior Notes [Member] | Carrying Amount [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior notes		$ 3,242		3,242
Senior Notes [Member] | Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior notes		$ 3,232		3,358
Purchased Call Options - 2021 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Premium paid				1
Purchased Call Options - 2021 [Member] | Not Designated as Hedging Instrument [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Premium paid				$ 1
2018 Credit Facility [Member] | Long-term Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Credit facility, maturity date	Apr. 26, 2023	Apr. 26, 2023
Amount to be amended, redeemed or refinanced to avoid acceleration	$ 700
2018 Credit Facility [Member] | Long-term Debt [Member] | Carrying Amount [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Credit facility		$ 360
2018 Credit Facility [Member] | Long-term Debt [Member] | Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Credit facility		$ 360