STOCK-BASED COMPENSATION

3 Months Ended

Mar. 31, 2018

NOTE 4. STOCK-BASED COMPENSATION

Presented below is a summary of the stock-based compensation cost and associated tax benefit included in the accompanying consolidated statements of operations:

	Three Months Ended
	March 31,
	2018		2017
Stock-based compensation expense	$	35.1	$	28.4
Tax benefit	$	7.2	$	9.1

During the first three months of 2018, the Company granted 0.2 million employee stock options, which had a weighted average grant date fair value of $45.87 per share based on the Black-Scholes option-pricing model. The Company also granted 0.7 million shares of restricted stock in the first three months of 2018, which had a weighted average grant date fair value of $167.50 per share. Both the employee stock options and restricted stock generally vest ratably over a four-year period. Additionally, the Company granted 0.1 million shares of performance-based awards whereby the number of shares that ultimately vest are based on the achievement of certain non-market based performance metrics of the Company over a three-year period. The weighted average grant date fair value of these awards was $162.42 per share.

The following weighted average assumptions were used in determining the fair value for options granted in 2018:

Expected dividend yield	1.05%
Expected stock volatility	25.6%
Risk-free interest rate	2.81%
Expected holding period	6.2 years
Grant date fair value	$45.87

Unrecognized stock-based compensation expense at March 31, 2018 was $11.7 million and $220.1 million for stock options and unvested restricted stock, respectively, which is expected to be recognized over a weighted average period of 1.4 years and 1.8 years, respectively. Additionally, there was $43.1 million of unrecognized stock-based compensation expense relating to the aforementioned non-market based performance-based awards, which is expected to be recognized over a weighted average period of 1.1 years.

The following tables summarize information relating to stock option exercises and restricted stock vesting:

	Three Months Ended
	March 31,
Exercise of stock options:	2018		2017
Proceeds from stock option exercises	$	26.6	$	20.6
Aggregate intrinsic value	$	61.9	$	21.6
Tax benefit realized upon exercise	$	15.0	$	7.9
Number of shares exercised		0.5		0.4

	Three Months Ended
	March 31,
Vesting of restricted stock:	2018		2017
Fair value of shares vested	$	146.7	$	106.8
Tax benefit realized upon vesting	$	33.9	$	33.7
Number of shares vested		0.9		0.9

	Three Months Ended
	March 31,
Vesting of performance-based restricted stock:	2018		2017
Fair value of shares vested	$	23.0	$	19.5
Tax benefit realized upon vesting	$	5.5	$	6.9
Number of shares vested		0.1		0.2