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Stock-based Compensation and Other Employee Benefit Plans (Tables)
12 Months Ended
Dec. 31, 2020
Share-based Payment Arrangement [Abstract]  
Share-based Payment Arrangement, Expensed and Capitalized, Amount
Total stock-based compensation expense for the years ended December 31, 2020, 2019 and 2018 was as follows:

 202020192018
Stock-based compensation included in SG&A expenses$32.3 $39.3 $31.5 
Excess tax benefits recognized from stock-based compensation$1.6 $1.1 $2.7 
Share-based Payment Arrangement, Restricted Stock Unit, Activity [Table Text Block]
A summary of the status of the Company’s unvested RSUs as of December 31, 2020 and changes during the year then ended are presented below (number of units in millions, except fair value per unit): 
 Service ConditionsPerformance/Market
and Service Conditions
TotalWeighted-Average Grant-Date Fair Value Per Unit
Unvested RSUs outstanding at December 31, 2019
0.5 0.7 1.2 $63.21 
Granted0.2 0.3 0.5 $61.23 
Vested(0.1)(0.4)(0.5)$59.51 
Unvested RSUs outstanding at December 31, 2020
0.6 0.6 1.2 $63.66 
Unvested and expected to vest RSUs outstanding at December 31, 2020
0.5 0.6 1.1 $63.51 
Fair Value Measurement Inputs and Valuation Techniques The fair value for the TSR Awards was $49.11 per share, which was determined on the grant date using a Monte Carlo simulation model based on the following assumptions:
Expected term (years)3.0
Dividend yield— 
Volatility factor38.8 %
Risk-free interest rate0.3 %
Schedule of Share-based Payment Award, Employee Stock Purchase Plan, Valuation Assumptions The fair values of the options granted under the ESPP were estimated using the Black-Scholes valuation model at the date of grant based on the following assumptions during the years ended December 31, 2020, 2019 and 2018:
 202020192018
Expected term (years)0.50.50.5
Dividend yield— — — 
Expected volatility
32.0 - 63.3%
25.0 - 38.5%
23.0 - 30.3%
Weighted-average risk-free interest rate
0.1 - 1.8%
2.1 - 2.4%
1.2 - 1.9%
Average Black-Scholes valuation per share$12.53 $17.11 $15.09 
Shares issued (millions)0.4 0.2 0.2 
Stock-based compensation expense (millions)$4.0 $4.1 $2.7