Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Stock-Based Compensation Expense

Stock based compensation expense for the years ended December 31, 2017, 2016 and 2015 was as follows (in millions):

	2017		2016		2015
Stock based compensation	$	83.1	$	78.8	$	61.8
Tax benefit recognized in net earnings	29.1		27.6		21.6
Windfall tax benefit, net	—		—		22.2

Weighted-Average Assumptions of Stock-Based Compensation

The weighted-average fair value of options granted in 2017, 2016 and 2015 were calculated using the following weighted-average assumptions:

	2017	2016	2015
Weighted-average fair value ($)	40.87	34.57	33.98
Risk-free interest rate (%)	2.03	1.44	1.53
Average expected option life (years)	5.26	5.20	5.10
Expected volatility (%)	18.74	21.35	22.17
Expected dividend yield (%)	0.67	0.70	0.62

Stock-Based Compensation Activity

The following table summarizes the Company's activities with respect to its share-based compensation plans for the years ended December 31, 2017 and 2016:

	Number of shares		Weighted-average exercise price per share		Weighted-average contractual term	Aggregate intrinsic value
Outstanding at January 1, 2016	3,117,616		$	104.54
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
Granted	608,598		210.56
Exercised	(644,610	)	95.14
Canceled	(187,721	)	170.75
Outstanding at December 31, 2017	3,195,864		140.68		6.09	$	368,589,147
Exercisable at December 31, 2017	1,766,869		$	103.48	4.12	$	269,474,477

Schedule of Stock-Based Compensation by Exercise Price Range

The following table summarizes information for stock options outstanding at December 31, 2017:

	Outstanding options				Exercisable options
Exercise price	Number	Average exercise price		Average remaining life (years)	Number	Average exercise price
$40.57 - 52.37	147,840	$	47.38	1.7	147,840	$	47.38
52.37 - 78.56	500,259	61.18		1.2	500,259	61.18
78.56 - 104.75	172,777	93.83		4.1	172,777	93.83
104.75 - 130.94	342,805	117.51		5.2	342,805	117.51
130.94 - 157.12	481,652	139.21		6.4	430,101	138.27
157.12 - 183.31	870,883	169.61		7.8	151,337	166.74
183.31 - 209.50	225,450	187.64		8.7	21,750	185.47
209.50 - 235.68	434,398	215.02		9.3	—	—
235.68 - 261.87	19,800	253.01		9.8	—	—
$40.57 - 261.87	3,195,864	$	140.68	6.1	1,766,869	$	103.48

Schedule of Nonvested Restricted Stock Awards Activity

A summary of the Company's nonvested shares activity for 2017 and 2016 is as follows:

	Number of shares		Weighted-average grant date fair value
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
Granted	410,267		205.88
Vested	(387,452	)	155.95
Forfeited	(116,491	)	173.53
Nonvested at December 31, 2017	858,996		$	187.01