Equity Incentive Plan (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Aggregate Intrinsic Value [Abstract]
Options, Outstanding, Intrinsic Value	$ 208.9	$ 157.4
Options, Exercisable, Intrinsic Value	$ 159.7
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options, Outstanding, Number, Beginning	2,394,938
Options, Grants in Period, Net of Forfeitures	182,506
Options, Exercises in Period	(410,019)
Options, Forfeitures in Period	(62,650)
Options, Outstanding, Number, Ending	2,104,775
Options, Exercisable, Number	1,337,939
Weighted Average Exercise Price [Abstract]
Options, Outstanding, Weighted Average Exercise Price, Beginning	$ 82.16
Options, Grants in Period, Weighted Average Exercise Price	$ 169.37
Options, Exercises in Period, Weighted Average Exercise Price	$ 53.48
Options, Forfeitures in Period, Weighted Average Exercise Price	$ 107.93
Options, Outstanding, Weighted Average Exercise Price, Ending	$ 94.45
Options, Exercisable, Weighted Average Exercise Price	$ 73.91