Debt and Credit Agreements Credit Facility (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Line of Credit Facility [Line Items]
Line of Credit Facility Commitment Increase		$ 250.0
Line of Credit Facility Limits on Letters of Credit		$ 200.0
Margin for base rate advances		0.30%
Margin for Eurocurrency rate advances		1.30%
Annual rate for fronting fees accrued on letters of credit		0.25%
Annual facility fee		0.20%
Leverage ratio maximum	[1]	3.50x
Interest coverage ratio minimum	[2]	5.00x
Committed credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 1,000.0	$ 1,000.0
Line of Credit Facility, Amount Outstanding		0.0	0.0
Letters of Credit Outstanding, Amount		3.7	16.0
Line of Credit Facility, Remaining Borrowing Capacity		996.3	984.0
Uncommitted credit facility
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		744.5	740.3
Line of Credit Facility, Amount Outstanding		150.1	107.2
Letters of Credit Outstanding, Amount		1.1	3.9
Line of Credit Facility, Remaining Borrowing Capacity		$ 593.3	$ 629.2
Line of Credit Facility Weighted Average Interest Rate		3.00%	5.00%

[1] The leverage ratio is defined as debt as of the last day of such fiscal quarter to EBITDA, as defined in the Credit Agreement, for the four quarters then ended. The leverage ratio may be changed to not more than 4.00 to 1 at our election for four consecutive fiscal quarters, beginning with the fiscal quarter in which there is an occurrence of one or more acquisitions with an aggregate purchase price of at least $200.0.

[2] The interest coverage ratio is defined as EBITDA, as defined in the Credit Agreement, to net interest expense.