Financing Financing (Short-Term Debt) (Details) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2015
Short-term Debt [Line Items]
Commercial Paper	$ 171,400,000	$ 0
Long-term Commercial Paper			$ 500,000,000
Long-term debt	937,100,000	494,100,000
Short-term borrowings and current maturities of long-term debt	171,400,000	249,400,000
Two point seven five Percent Notes Due 2018 [Member]
Short-term Debt [Line Items]
Debt Instrument, Face Amount		250,000,000
Other Debt [Member] [Member]
Short-term Debt [Line Items]
Amortization of Debt Issuance Costs		600,000
Line of Credit [Member]
Short-term Debt [Line Items]
Amortization of Debt Issuance Costs	$ 2,000,000	2,400,000
Revolving Credit Facility [Member] | Line of Credit [Member] | 2017 Facility [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 550,000,000