Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2016

Stock based compensation expense for the years ended December 31, 2016, 2015 and 2014 was as follows (in millions):

	2016		2015		2014
Stock based compensation	$	78.8	$	61.8	$	63.0
Tax benefit recognized in net income		27.6		21.6		22.1
Windfall tax benefit, net		-		22.2		21.5

Windfall tax benefits are no longer calculated due to the adoption of the ASU related to stock compensation (see Note 1), as all tax benefits are recognized in net income.

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 2016, 2015 and 2014 were calculated using the following weighted-average assumptions:

	2016		2015		2014
Weighted-average fair value ($)		34.57		33.98		34.95
Risk-free interest rate (%)		1.44		1.53		1.63
Average expected option life (years)		5.20		5.10		5.22
Expected volatility (%)		21.35		22.17		27.01
Expected dividend yield (%)		0.70		0.62		0.58

Schedule of Share-based Compensation, Stock Option Activity

The following table summarizes the Company's activities with respect to its share-based compensation plans for the years ended December 31, 2016 and 2015:

	Number of shares			Weighted-average exercise price per share		Weighted-average contractual term		Aggregate intrinsic value
Outstanding at January 1, 2015		2,981,111		$	90.48
Granted		628,155			162.77
Exercised		(400,050	)		82.50
Canceled		(91,600	)		142.36
Outstanding at December 31, 2015		3,117,616			104.54		6.08		$	265,782,636
Granted		743,250			172.23
Exercised		(371,853	)		75.23
Canceled		(69,416	)		159.97
Outstanding at December 31, 2016		3,419,597			121.31		6.15		$	211,369,740
Exercisable at December 31, 2016		1,954,306		$	89.37		4.28		$	183,136,309

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

The following table summarizes information for stock options outstanding at December 31, 2016:

		Outstanding options						Exercisable options
Exercise price		Number		Average exercise price		Average remaining life (years)		Number		Average exercise price
$	38.46 - 57.68		689,289	$	53.28		1.5		689,289	$	53.28
	57.69 - 76.91		259,460		72.55		4.2		259,460		72.55
	76.92 - 96.14		249,281		93.34		5.0		249,281		93.34
	96.15 - 115.37		283,069		114.99		6.0		283,069		114.99
	115.38 - 134.60		503,778		130.72		7.0		368,456		129.96
	134.61- 153.82		259,370		144.19		7.7		75,334		141.95
	153.83 - 173.05		916,725		167.80		8.8		25,334		157.81
	173.06 - 192.28		258,625		179.42		9.5		4,083		175.47
$	38.46 - 192.28		3,419,597	$	121.31		6.2		1,954,306	$	89.37

Schedule of Nonvested Restricted Stock Awards Activity

Restricted Stock Grants - During 2016 and 2015, the Company granted 555,730 and 437,035 shares, respectively, of restricted stock to certain employee and director participants under its share-based compensation plans. Restricted stock grants generally vest over a period of 1 to 3 years. The Company recorded $57.8 million, $46.5 million and $46.4 million of compensation expense related to outstanding shares of restricted stock held by employees and directors during 2016, 2015 and 2014, respectively. A summary of the Company's nonvested shares activity for 2016 and 2015 is as follows:

	Number of shares			Weighted-average grant date fair value
Nonvested at December 31, 2014		542,555		$	130.29
Granted		437,035			159.32
Vested		(243,423	)		183.10
Forfeited		(26,892	)		148.82
Nonvested at December 31, 2015		709,275		$	146.64
Granted		555,730			172.67
Vested		(287,233	)		141.27
Forfeited		(25,100	)		139.56
Nonvested at December 31, 2016		952,672		$	164.62