Fair Value of Financial Instruments Fair Value of Financial Instruments (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	$ 0	$ 0	$ 0	$ 0
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Transfers, Net	0	$ 0	0	$ 0
Cash Surrender Value, Fair Value Disclosure	28,000,000		28,000,000		$ 26,000,000
Long-term Debt	2,377,000,000		2,377,000,000		2,350,000,000
Unamortized Debt Issuance Expense	9,000,000		9,000,000		11,000,000
Long-term Debt, Fair Value	2,763,000,000		2,763,000,000		2,693,000,000
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt, Fair Value	2,663,000,000		2,663,000,000		2,543,000,000
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt, Fair Value	$ 100,000,000		$ 100,000,000		$ 150,000,000