Debt and Credit Agreements Credit Agreements (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Cash debt pooling arrangements, amount netted	$ 2,274.9	$ 2,065.8
Margin for base rate advances	0.125%
Margin for Eurocurrency rate advances	1.125%
Annual rate for fronting fees accrued on letters of credit	0.25%
Annual facility fee	0.125%
Leverage ratio maximum	3.75x
Leverage Ratio Acquisition Price Threshold	$ 200.0
Committed credit facility [Member]
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	1,500.0
Line of credit facility, available capacity increase amount	250.0
Limits on letters of credit	50.0
Line of credit facility, amount outstanding	0.0
Letters of credit, amount outstanding	8.4	8.5
Line of credit facility, remaining borrowing capacity	1,491.6	1,491.5
Uncommitted credit facility
Line of Credit Facility [Line Items]
Line of credit facility, amount outstanding	52.4	73.7
Line of Credit Facility, Average Outstanding Amount	88.0	96.4
Line of credit facility, current borrowing capacity	$ 1,056.0	$ 1,173.1
Line of credit facility, weighted average interest rate, over time	5.20%	4.50%