Schedule of Computation of Basic and Diluted EPS under Two-class Method (Detail) - 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
Basic and diluted:
Net (loss) income attributable to controlling interest		$ (174.7)	$ 109.1	$ (99.9)	$ 220.5
Net income applicable to common shareholders		(174.7)	109.1	(99.9)	220.5
Earnings allocated to participating share awards	[1]	(0.0)	(0.0)	(0.0)	(0.0)
Net income attributable to common shareholders		$ (174.7)	$ 109.1	$ (99.9)	$ 220.5
Denominator:
Basic: Weighted average common stock	[1]	87.3	87.2	87.3	87.2
Add: Weighted average stock options/share awards	[1]	0.0	0.1	0.0	0.2
Diluted:	[2]	87.3	87.3	87.3	87.4
Net (loss) earnings per share - basic	[3]	$ (2.00)	$ 1.25	$ (1.14)	$ 2.53
Net (loss) earnings per share - diluted	[2],[3]	$ (2.00)	$ 1.25	$ (1.14)	$ 2.52

[1] The Company’s unvested RSUs and PSUs, of which some included the right to receive non-forfeitable dividend equivalents, are considered participating securities. Calculations of EPS under the two-class method exclude from the numerator any dividends paid or owed on participating securities and any undistributed earnings considered to be attributable to participating securities. The related participating securities are similarly excluded from the denominator

[2] Shares in the diluted loss per share calculation for the three and six month periods ended June 30, 2020 represent basic shares due to the net loss.

[3] Participating share awards with the right to receive dividend equivalents are (under the two-class method) excluded from the earnings per share calculation (see Note 11 to the unaudited condensed consolidated financial statements).