Debt - Revolving Loan Arrangements (Details) $ in Millions	Jun. 30, 2018 USD ($)
Revolving lines of credit
Total Amount Committed by Lenders	$ 750.5
Outstanding Letters of Credit	124.5
Total Amount Available	626.0
Other lines of credit
Revolving lines of credit
Total Amount Committed by Lenders	250.5
Outstanding Letters of Credit	123.4
Total Amount Available	$ 127.1
2015 Credit Agreement | US Dollar revolving loan
Revolving lines of credit
Weighted Average Interest Rate (as a percent)	0.00%
Total Amount Committed by Lenders	$ 500.0
Outstanding Letters of Credit	1.1
Total Amount Available	$ 498.9