Accounting Policies - Recently Issued Accounting Standards (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Recognition of tax benefit		$ 4
Unamortized deferred financing fees		$ 45		$ 48
Adjustments for New Accounting Pronouncement | Prepaid Expenses and Other Current Assets
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Unamortized deferred financing fees				(15)
Adjustments for New Accounting Pronouncement | Other Assets
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Unamortized deferred financing fees				(33)
Adjustments for New Accounting Pronouncement | Long Term Debt and Capital Leases Due Within One Year
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Unamortized deferred financing fees				2
Adjustments for New Accounting Pronouncement | Long Term Debt and Capital Leases
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Unamortized deferred financing fees				46
Adjustments for New Accounting Pronouncement | Interest Expense
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Amortization of financing fees	$ 3		$ 11
Adjustments for New Accounting Pronouncement | Other (Income) Expense
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Amortization of financing fees	$ (3)		$ (11)
New Accounting Pronouncement, Early Adoption, Effect | Retained Earnings | Accounting Standards Updated 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment				$ 56