Share-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2020

Share-based Payment Arrangement [Abstract]

Share-based compensation expense

Share-based compensation expense and cash flow amounts were as follows:

	Year Ended December 31,
	2020		2019		2018
	(Dollars in millions)
Share-based compensation expense	$	13.5	$	38.3	$	34.9
Tax benefit	—		—		—
Share-based compensation expense, net of tax benefit	$	13.5	$	38.3	$	34.9
Cash received upon the exercise of stock options	—		—		—
Write-off tax benefits related to share-based compensation	—		—		—

Schedule of Share-based Compensation, Restricted Stock Units Activity

A summary of restricted stock unit activity is as follows:

	Year Ended December 31, 2020	Weighted Average Grant-Date Fair Value
Nonvested at December 31, 2019	1,706,025	$	26.89
Granted	1,706,907	9.71
Vested	(1,105,979)	24.37
Forfeited	(676,997)	16.38
Nonvested at December 31, 2020	1,629,956	$	14.49

Schedule of Performance Units Activity

A summary of performance unit activity is as follows:

	Year Ended December 31, 2020	Weighted Average Remaining Contractual Life
Nonvested at December 31, 2019	426,606	1.6
Granted	686,082
Vested	—
Forfeited	(254,100)
Nonvested at December 31, 2020	858,588	1.5

Schedule of Share-based Payment Award, Performance Units, Valuation Assumptions

The assumptions used in the valuations for grants were as follows:

	Year Ended December 31,
	2020		2019
Risk-free interest rate	1.45	%	2.44	%
Expected volatility	49.34	%	48.81	%
Dividend yield	—	%	—	%