Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2014

Stock based compensation expense for the years ended December 31, 2014, 2013 and 2012 was as follows (in millions):

	2014		2013		2012
Stock based compensation	$	63.0	$	53.4	$	40.8
Tax benefit recognized in net income		22.1		18.7		14.3
Windfall tax benefit, net		21.5		16.0		30.8

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions

The Company estimates the fair value of its option awards using the Black-Scholes option valuation model. The stock volatility for each grant is measured using the weighted-average of historical daily price changes of the Company's common stock over the most recent period equal to the expected life of the grant. The expected term of options granted is derived from historical data to estimate option exercises and employee forfeitures, and represents the period of time that options granted are expected to be outstanding. The risk-free rate for periods within the contractual life of the option is based on the U.S. Treasury yield curve in effect at the time of grant. The weighted-average fair value of options granted in 2014, 2013 and 2012 were calculated using the following weighted-average assumptions:

	2014		2013		2012
Weighted-average fair value ($)		34.95		37.08		30.25
Risk-free interest rate (%)		1.63		0.86		0.77
Average expected option life (years)		5.22		5.19		5.24
Expected volatility (%)		27.01		36.09		36.51
Expected dividend yield (%)		0.58		0.56		0.58

Schedule of Share-based Compensation, Stock Option Activity

The following table summarizes the Company's activities with respect to its stock option plans for the years ended December 31, 2014 and 2013:

	Number of shares			Weighted-average exercise price per share		Weighted-average contractual term		Aggregate intrinsic value
Outstanding at January 1, 2013		2,918,195		$	63.15
Granted		601,350			117.78
Exercised		(424,945	)		56.48
Canceled		(106,164	)		98.74
Outstanding at December 31, 2013		2,988,436			74.00		6.22		$	193,279,214
Granted		650,000			137.05
Exercised		(587,661	)		55.98
Canceled		(69,664	)		116.29
Outstanding at December 31, 2014		2,981,111			90.48		6.37		$	196,378,239
Exercisable at December 31, 2014		1,811,238		$	68.02		4.91		$	159,978,254

Summary of Options Outstanding and Exercisable, by Range of Exercise Prices

The following table summarizes information for stock options outstanding at December 31, 2014:

		Outstanding options						Exercisable options
Exercise price		Number		Average exercise price		Average remaining life (years)		Number		Average exercise price
$	31.66 - 47.49		110,598	$	41.82		4.2		110,598	$	41.82
	47.50 - 63.32		911,913		54.10		3.3		911,913		54.10
	63.33 - 79.15		379,830		72.62		6.1		379,830		72.62
	79.16 - 94.98		325,632		92.70		7.0		216,610		92.24
	94.99 - 110.81		89,049		97.99		7.5		51,717		98.07
	110.82- 126.64		512,589		117.12		8.2		124,727		116.27
	126.65 - 142.47		573,000		135.14		9.2		15,843		133.77
	142.48 - 158.30		78,500		150.38		9.7		-		-
$	31.66 - 158.30		2,981,111	$	90.48		6.4		1,811,238	$	68.02

Schedule of Nonvested Restricted Stock Awards Activity

Restricted Stock Grants - During 2014 and 2013, the Company granted 375,060 and 399,540 shares, respectively, of restricted stock to certain employee and director participants under the 2006 Plan. Restricted stock grants generally vest over a period of 1 to 3 years. The Company recorded $46.4 million, $36.5 million and $25.9 million of compensation expense related to outstanding shares of restricted stock held by employees and directors during 2014, 2013 and 2012, respectively. A summary of the Company's nonvested shares activity for 2014 and 2013 is as follows:

	Number of shares			Weighted-average grant date fair value
Nonvested at December 31, 2012		571,905		$	80.96
Granted		399,540			117.74
Vested		(373,946	)		126.80
Forfeited		(23,649	)		124.48
Nonvested at December 31, 2013		573,850		$	103.44
Granted		375,060			142.30
Vested		(378,994	)		153.16
Forfeited		(27,361	)		106.60
Nonvested at December 31, 2014		542,555		$	130.29