Debt and Credit Agreements Credit Facility (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
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	0.275%
Margin for Eurocurrency rate advances	1.275%
Annual rate for fronting fees accrued on letters of credit	0.25%
Line of Credit Facility, Commitment Fee Percentage	0.225%
Leverage ratio maximum	3.25x	[1]
Interest coverage ratio minimum	5.00x	[2]
Cash debt pooling arrangements, amount netted	1,590.7		1,415.3
Committed credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Remaining Borrowing Capacity	984.0		985.7
Line of Credit Facility, Maximum Borrowing Capacity	1,000.0		1,000.0
Long-term Line of Credit	0		0
Letters of Credit Outstanding, Amount	16.0		14.3
Uncommitted credit facility
Line of Credit Facility [Line Items]
Line of Credit Facility Weighted Average Interest Rate	4.50%		4.50%
Line of Credit Facility, Remaining Borrowing Capacity	629.2		516.9
Line of Credit Facility, Maximum Borrowing Capacity	740.3		700.2
Long-term Line of Credit	107.2		179.1
Letters of Credit Outstanding, Amount	$ 3.9		$ 4.2

[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.

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