STOCK-BASED COMPENSATION

9 Months Ended

Sep. 30, 2019

Share-based Payment Arrangement, Noncash Expense [Abstract]

STOCK-BASED COMPENSATION

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 September 30,				Nine Months Ended September 30,
	2019		2018		2019		2018
Stock-based compensation cost	$	33.3	$	30.5	$	103.2	$	100.0
Tax benefit	$	6.9	$	11.5	$	22.0	$	26.0

During the first nine months of 2019, the Company granted 0.2 million employee stock options, which had a weighted average grant date fair value of $43.10 per share based on the Black-Scholes option-pricing model. The Company also granted 0.8 million shares of restricted stock in the first nine months of 2019, which had a weighted average grant date fair value of $173.71 per share. Both the employee stock options and restricted stock generally vest ratably over four years. 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 three years. The weighted average grant date fair value of these awards was $168.04 per share.

The following weighted average assumptions were used in determining the fair value for options granted in 2019:

Expected dividend yield	1.15	%
Expected stock volatility	23.61	%
Risk-free interest rate	2.59	%
Expected holding period	6.2 years

Unrecognized stock-based compensation expense at September 30, 2019 was $7.5 million and $175.9 million for stock options and unvested restricted stock, respectively, which is expected to be recognized over a weighted average period of 2.1 years and 2.5 years, respectively. Additionally, there was $29.6 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 1.9 years.

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

	Nine Months Ended September 30,
	2019		2018
Exercise of stock options:
Proceeds from stock option exercises	$	28.9	$	36.2
Aggregate intrinsic value	$	99.2	$	94.9
Tax benefit realized upon exercise	$	24.3	$	23.2
Number of shares exercised	0.7		0.8
Vesting of restricted stock:
Fair value of shares vested	$	152.7	$	150.0
Tax benefit realized upon vesting	$	36.2	$	34.7
Number of shares vested	0.8		0.9
Vesting of performance-based restricted stock:
Fair value of shares vested	$	47.5	$	23.0
Tax benefit realized upon vesting	$	11.5	$	5.6
Number of shares vested	0.3		0.1