STOCKHOLDERS' EQUITY (Tables)

12 Months Ended

Dec. 31, 2019

STOCKHOLDERS' EQUITY

Schedule of stock-based compensation expense

	Years Ended December 31,
	2019		2018		2017
	(in millions)
Cost of operations	$	16.5	$	23.3	$	18.8
General and administrative		8.6		21.1		22.5
Total	$	25.1	$	44.4	$	41.3

Summary of stock option activity

	Outstanding			Exercisable
		Weighted			Weighted
		Average			Average
	Options	Exercise Price		Options	Exercise Price
Balance at January 1, 2017	18,866	$	37.60	18,864	$	37.60
Options granted	—		—
Options exercised	(7,004)		60.85
Options forfeited	(3)		35.56
Balance at December 31, 2017	11,859	$	23.87	11,859	$	23.87
Options granted	—		—
Options exercised	(886)		12.70
Options forfeited	(119)		2.74
Balance at December 31, 2018	10,854	$	25.01	10,854	$	25.01
Options granted	—		—
Options exercised	(10,854)		25.01
Options forfeited	—		—
Balance at December 31, 2019	—	$	—	—	$	—