Short-Term Borrowings And Long-Term Debt (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Short-term borrowings	$ 0		$ 0		$ 1.2
Maturity of credit facility			June 2016
Amount of borrowing from credit facility	0		0		0
Maximum amount of outstanding borrowings and letters of credit	500.0		500.0
Line of credit facility maximum amount, increase net	750.0		750.0
Estimated debt, fair value	1,566.4		1,566.4
Interest expense	14.5	13.0	28.9	25.9
Interest income	2.3	1.4	3.6	2.2
Credit facility, commitment fee percentage			0.20%
Credit facility, commitment fee amount			$ 500.0
2011 Credit Facility [Member]
Credit facility weighted average interest rate		2.59%		2.61%
Maximum [Member]
Debt to EBITDA ratio maximum limit			3.25
Range of margin added to base rate	1.45%		1.45%
Minimum [Member]
Consolidated EBITDA to consolidated interest expense minimum limit			3.0
Range of margin added to base rate	0.075%		0.075%