Earnings/(Loss) Per Share - EPS Computation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020		Dec. 31, 2019
Numerator:
Net income/(loss)	$ 7.5	$ (12.6)	$ 6.5	$ (0.8)	$ (3.7)	$ (10.5)	$ (0.2)	$ (1.9)	$ 0.6	$ (16.3)	[1]	$ 50.2
Adjustment for interest on 2025 Notes, net of tax									0.2	0.0		0.0
Net income/(loss) after assumed conversion of 2025 Notes									0.8	(16.3)		50.2
Net income/(loss) after assumed conversion of 2025 Notes									$ 0.8	$ (16.3)		$ 50.2
Denominator:
Weighted average common shares outstanding - basic (in shares)	161,700	161,600	148,700	146,500	146,300	146,300	146,200	146,100	154,700	146,200	[2]	146,000
Dilutive share equivalents from share-based plans (in shares)									1,500	0		400
Weighted average common share equivalents (in shares)									28,100	0		0
Weighted average common shares outstanding – diluted (in shares)	191,600	161,600	178,000	146,500	146,300	146,300	146,200	146,100	184,300	146,200	[2]	146,400
Basic earnings/(loss) per common share:
Net (loss)/income per weighted average share - basic (in dollars per share)	$ 0.05	$ (80,000.00)	$ 40,000.00	$ (10,000.00)	$ (30,000.00)	$ (70,000.00)	$ 0	$ (10,000.00)		$ (0.11)	[2]	$ 0.34
Diluted earnings/(loss) per common share:
Net (loss)/income per weighted average share- diluted (in dollars per share)	$ 0.04	$ (80,000.00)	$ 30,000.00	$ (10,000.00)	$ (30,000.00)	$ (70,000.00)	$ 0	$ (10,000.00)		$ (0.11)	[2]	$ 0.34
Capitalized interest costs									$ 15.4	$ 12.0		$ 5.7
Convertible Debt
Diluted earnings/(loss) per common share:
Capitalized interest costs									$ 11.4	$ 5.7

[1] As adjusted for the adoption of ASU 2020-06 using the full retrospective method.

[2] As adjusted for the adoption of ASU 2020-06 using the full retrospective method.