Equity (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		0 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Feb. 26, 2013 Restricted stock, 2013 grant
Equity
Issuance of common stock in connection with the exercise of employee stock options (in shares)	605,016
Total proceeds from the exercise of employee stock options	$ 31.6	$ 4.6
Share Based Compensation
Restricted stock granted (in shares)			324,780
The number of grants made during the period on the basis service and performance criteria other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).			134,725
Fair value of restricted stock granted (in dollars per share)			$ 65.73
Share of common stock			1
Share Repurchase Program
Remaining number of common stock authorized for repurchase under stock repurchase program (in shares)	7,883,033
Number of shares repurchased under stock repurchase program	0	0