Condensed Quarterly Revenues and Earnings (Unaudited) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Schedule of Quarterly Financial Information [Line Items]
Revenues	$ 1,373.9	[1]	$ 1,390.3	[1]	$ 1,345.3	[1]	$ 1,225.4	[1]	$ 1,219.2	[1]	$ 1,191.1	[1]	$ 1,161.5	[1]	$ 1,070.0	[1]	$ 5,334.9	$ 4,641.8	$ 4,141.4
Gross profit	222.5	[1]	225.7	[1]	222.6	[1]	206.7	[1]	194.5	[1]	194.2	[1]	191.8	[1]	184.5	[1]	877.5	765.0	700.3
Net income	$ 26.9		$ 22.7		$ 27.0		$ 32.5		$ 22.8	[1]	$ 20.7	[1]	$ 21.1	[1]	$ 17.6	[1]	$ 109.1	$ 82.2	$ 67.9
Net income per share:
Basic (in dollars per share)	$ 0.88		$ 0.74		$ 0.88		$ 1.05		$ 0.74	[2]	$ 0.67	[2]	$ 0.68	[2]	$ 0.57	[2]	$ 3.55	$ 2.64	$ 2.14
Diluted (in dollars per share)	$ 0.87		$ 0.73		$ 0.87		$ 1.04		$ 0.73	[2]	$ 0.66	[2]	$ 0.67	[2]	$ 0.56	[2]	$ 3.51	$ 2.61	$ 2.08

[1] Quarterly revenues, gross profit and net income may not agree to previously reported amounts on Form 10-Q as a result of subsequent discontinued operations or reclassifications of amounts in order to conform to current presentation.

[2] The sum of income per common share for the four quarters does not equal total income per common share due to changes in the average number of shares outstanding during the respective periods.