Stock Based Compensation (Tables)

6 Months Ended

Jun. 30, 2018

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

Stock Based Compensation Expense

The following table provides information regarding the Company's stock-based compensation expense:

	Three months ended June 30,				Six months ended June 30,
	2018		2017		2018		2017
Stock-based compensation	$	28.0	$	22.8	$	54.0	$	43.9
Tax effect recognized in net earnings	5.9		8.0		11.3		15.4

Weighted Average Assumptions Used to Value Option Grants

The following weighted average assumptions were used to estimate the fair value of options granted during current and prior year periods using the Black-Scholes option-pricing model:

	Six months ended June 30,
	2018	2017
Risk-free interest rate (%)	2.63	2.05
Expected option life (years)	5.32	5.27
Expected volatility (%)	18.02	18.81
Expected dividend yield (%)	0.59	0.68