Stock-based Compensation and Other Employee Benefit Plans (Tables)

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block]

Stock-based compensation expense in the accompanying consolidated statements of operations and comprehensive income was as follows:

	Year ended December 31,
	2023		2022		2021
Continuing operations (included in SG&A expenses)	$	44.0	$	49.3	$	39.6
Discontinued operations	—		—		13.1
	$	44.0	$	49.3	$	52.7

Fair Value Measurement Inputs and Valuation Techniques

The fair value of each RSU is based on the grant-date fair market value of the awards. The fair value of the Company's RSUs, other than the TSR components thereof, were determined on the grant date based on the closing market price for the Company's stock. The fair values of the TSR components of the awards were $6.41, $8.71, and $13.90 per share for the 2023, 2022 and 2021 awards, respectively, determined on the grant date using a Monte Carlo simulation model based on the following assumptions:

	2023		2022		2021
Expected term (years)	3.0		3.0		3.0
Dividend yield	—		—		—
Volatility factor	36.0	%	43.9	%	46.0	%
Risk-free interest rate	3.7	%	1.8	%	0.3	%

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, 2023 and changes during the year then ended are presented below (number of units in millions, except fair value per unit): 

	Service Conditions	Performance/Market and Service Conditions	Total	Weighted-Average Grant-Date Fair Value Per Unit
Unvested RSUs outstanding at December 31, 2022	0.5	0.2	0.7		$	92.13
Granted	0.4	0.7	1.1		$	76.69
Vested	(0.3)	(0.3)	(0.6)		$	72.70
Unvested RSUs outstanding at December 31, 2023	0.6	0.6	1.2
Unvested and expected to vest RSUs outstanding at December 31, 2023	0.6	0.5	1.1		$	92.83

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:

	Year Ended December 31,
	2023		2022		2021
Expected term (years)	0.5		0.5		0.5
Dividend yield	—		—		—
Expected volatility	38.1 - 38.7%		27.8 - 32.4%		39.2 - 55.2%
Weighted-average risk-free interest rate	3.8 - 4.7%		0.1 - 1.0%		0.1 - 0.1%
Average Black-Scholes valuation per share	$	23.01	$	27.60	$	21.70
Shares issued (millions)	0.3		0.2		0.2
Stock-based compensation expense (millions)	$	6.1	$	6.2	$	4.9