Financing Arrangements and Debt (Narrative) (Details) - USD ($)	9 Months Ended
	Sep. 30, 2017	Aug. 31, 2017	Aug. 31, 2016
Line of Credit Facility [Line Items]
Capital Lease Duration	25 years
Capital lease payment duration	15 years
Capital lease expiration date	Mar. 31, 2029
Capital lease obligations, current	$ 9,800,000
Capital lease obligations, noncurrent	$ 136,500,000
5.75% Notes, Due August 15, 2025 [Member]
Line of Credit Facility [Line Items]
Face amount of notes		$ 550,000,000
Notes payable, stated interest rate		5.75%
Maturity date	Aug. 15, 2025
Transaction costs		$ 8,200,000
2.50% Notes, Due December 2017 [Member]
Line of Credit Facility [Line Items]
Notes payable, stated interest rate		2.50%
6.875 Notes, Due August 15, 2024 [Member]
Line of Credit Facility [Line Items]
Face amount of notes			$ 550,000,000
Notes payable, stated interest rate			6.875%
Maturity date	Aug. 15, 2024
2016 Senior Unsecured Guaranteed Credity Facility [Member]
Line of Credit Facility [Line Items]
Credit facility maximum borrowing capacity	$ 1,100,000,000		$ 1,200,000,000
Credit facility, expiration date	Aug. 01, 2019
Amount outstanding	$ 0
Transaction costs			14,000,000
2016 Senior Unsecured Guaranteed Credity Facility [Member] | Eurodollar [Member]
Line of Credit Facility [Line Items]
Interest rate	4.50%
2016 Senior Unsecured Guaranteed Credity Facility [Member] | Letter of Credit [Member]
Line of Credit Facility [Line Items]
Amount outstanding	$ 84,800,000
2011 Unscured Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Credit facility maximum borrowing capacity	$ 630,000,000		$ 2,000,000,000