Reconciliation of Net Income and Number of Shares Used in Computing Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Numerator:
Net loss attributable to common shares	$ (162.4)	$ (544.1)	$ (264.0)	$ (2,854.4)
Denominator:
Weighted average basic and diluted shares outstanding	42.7	42.6	42.7	42.6
Net loss	$ (3.80)	$ (12.76)	$ (6.18)	$ (66.98)
Restricted Stock Units (RSUs)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount			0.3	0.5
Share-based Payment Arrangement, Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount			0.8	1.0