Fair Value Measurements (Carrying Amount And Estimated Fair Values Of Financial Instruments) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended	12 Months Ended
	Mar. 31, 2017	Jun. 30, 2016	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments, net	$ (229)		$ (375)
Carrying Amount [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	1,382		1,423
Senior notes	3,141		3,166
Derivative instruments, net	(229)		(375)
Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	1,382		1,423
Senior notes	3,088		3,182
Derivative instruments, net	$ (229)		$ (375)
Long-term Debt [Member] | Term Loan 1 due December 2020 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maturity date, year and month	2020-12	2018-11	2020-12
Accelerated maturity date, year and month if not amended, redeemed or refinanced	2019-10
Long-term Debt [Member] | Term Loan 2 due December 2020 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maturity date, year and month	2020-12		2020-12
Accelerated maturity date, year and month if not amended, redeemed or refinanced	2019-10
Long-term Debt [Member] | 2020 Senior Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maturity date, year and month	2020-01		2020-01
Amount to be amended, redeemed or refinanced to avoid acceleration	$ 765		$ 765
Long-term Debt [Member] | Carrying Amount [Member] | Term Loan 1 due December 2020 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	327		327
Long-term Debt [Member] | Carrying Amount [Member] | Term Loan 2 due December 2020 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	1,191		1,191
Long-term Debt [Member] | Fair Value [Member] | Term Loan 1 due December 2020 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	327		327
Long-term Debt [Member] | Fair Value [Member] | Term Loan 2 due December 2020 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	1,191		$ 1,191
Sold Call Options - 2017 [Member] | Not Designated as Hedging Instrument [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Premium paid	$ 5