Stock Based Compensation Plans

6 Months Ended

Jun. 30, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock Based Compensation Plans

8. Stock Based Compensation Plans

The following table provides a summary of option activity:

						Weighted
						Average
				Weighted		Remaining
				Average		Contractual		Aggregate
				Exercise		Term		Intrinsic
	Options			Price		(in Years)		Value
Outstanding at December 31, 2017		16.1		$	33.11
Granted		1.9			50.22
Exercised		(1.5	)		19.28
Cancelled		(0.1	)		47.73
Outstanding at June 30, 2018		16.4		$	36.22		5.8	$	279.5
Exercisable at June 30, 2018		10.5		$	29.19		4.3	$	251.8

The following table provides information regarding the intrinsic value of stock options exercised and stock compensation expense related to stock option awards:  

	Three Months Ended				Six Months Ended
	June 30,		June 30,		June 30,		June 30,
	2018		2017		2018		2017
Intrinsic Value of Stock Options Exercised	$	15.2	$	7.5	$	45.2	$	34.7
Stock Compensation Expense Related to Stock Option Awards	$	12.3	$	9.0	$	15.0	$	10.7
Issued Stock Options		1.9		1.8		1.9		1.8
Weighted Average Fair Value of Stock Options issued (per share)	$	9.63	$	9.70	$	9.63	$	9.67
Fair Value of Stock Options Issued	$	18.0	$	17.1	$	18.1	$	17.5

The following table provides a summary of the assumptions used in the valuation of issued stock options:

	Three Months Ended						Six Months Ended
	June 30,			June 30,			June 30,			June 30,
	2018			2017			2018			2017
Risk-free interest rate		2.9	%		2.1	%		2.9	%		2.1	%
Expected life in years		7.3			7.2			7.3			7.2
Expected volatility		17.1	%		16.9	%		17.1	%		16.9	%
Dividend yield		1.7	%		1.4	%		1.7	%		1.4	%