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
		Mar. 31, 2018	Mar. 31, 2017
Basic and diluted:
Net income attributable to controlling interest		$ 126.7	$ 143.9
Net income available to common shareholders		126.7	143.9
Earnings allocated to participating share awards	[1]		(0.1)
Net income attributable to common shareholders		$ 126.7	$ 143.8
Denominator:
Basic: Weighted average common stock	[1]	87.0	88.3
Add: Weighted average stock options/share awards	[1]	0.3	0.2
Diluted:	[1]	87.3	88.5
Basic EPS	[2]	$ 1.46	$ 1.63
Diluted EPS	[2]	$ 1.45	$ 1.62

[1] The Company’s unvested RSUs and PSs, of which some include 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] 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 16 to the unaudited condensed consolidated financial statements).