Net Income (loss) per common share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Numerator:
Net income (loss)	$ (67.0)	$ (87.1)	$ (52.9)	$ (4.6)	$ 193.1	$ (40.4)	$ (0.5)	$ 67.3	$ (211.6)	$ 219.5	$ 305.8
Denominator:
Weighted-average number of shares-basic (in shares)									50.1	53.5	52.7
Dilutive securities-equity awards (in shares)									0.0	0.6	1.1
Weighted-average number of shares-diluted (in shares)									50.1	54.1	53.8
Net income (loss) per common share - basic (in dollars per share)	$ (1.34)	$ (1.75)	$ (1.06)	$ (0.09)	$ 3.62	$ (0.75)	$ (0.01)	$ 1.26	$ (4.22)	$ 4.10	$ 5.80
Net income (loss) per common share - diluted (in dollars per share)	$ (1.34)	$ (1.75)	$ (1.06)	$ (0.09)	$ 3.60	$ (0.75)	$ (0.01)	$ 1.23	$ (4.22)	$ 4.06	$ 5.68
Anti-dilutive stock awards (in shares)									2.8	1.0	0.0