Credit Facilities (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2020	Jun. 30, 2020
Committed credit facility [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 1,500.0
Line of Credit Facility, Available Capacity Increase Amount		250.0
Line of Credit Facility, Limit on Letters of Credit		50.0
Line of Credit Outstanding, Amount		0.0
Letters of Credit Outstanding, Amount		8.3
Line of Credit Facility, Remaining Borrowing Capacity		1,491.7
Uncommitted credit facility [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		928.4
Line of Credit Outstanding, Amount		51.9
Line of Credit Facility, Average Outstanding Amount		$ 76.4
Short-term Debt, Weighted Average Interest Rate, over Time		3.70%
364 Day [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 500.0
Margin for base rate advances		0.25%
Margin for Eurocurrency rate advances		1.25%
Line of Credit Facility, Commitment Fee Percentage	0.25%
Line of Credit Facility, Fair Value of Amount Outstanding		$ 0.0