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		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Basic and diluted:
Net Income from continuing operations		$ 117.5	$ 105.7	$ 468.9	$ 389.3
Net Loss from discontinued operations (Note 3)			(14.9)	(187.5)	(24.8)
Net income attributable to controlling interest		117.5	90.8	281.4	364.5
Net income available to common shareholders		117.5	90.8	281.4	364.5
Net income attributable to common shareholders		$ 117.5	$ 90.8	$ 281.4	$ 364.5
Denominator:
Basic: Weighted average common stock		87.1	86.9	87.1	87.7
Add: Weighted average stock options/share awards		0.3	0.3	0.2	0.2
Diluted:		87.4	87.2	87.3	87.9
Basic EPS:
Continuing operations	[1]	$ 1.35	$ 1.22	$ 5.38	$ 4.44
Discontinued operations	[1]		(0.17)	(2.15)	(0.28)
Basic earnings per share		1.35	1.05	3.23	4.16
Diluted EPS:
Continuing operations	[1]	1.34	1.21	5.37	4.43
Discontinued operations	[1]		(0.17)	(2.15)	(0.28)
Diluted earnings per share		$ 1.34	$ 1.04	$ 3.22	$ 4.15

[1] 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 14 to the unaudited condensed consolidated financial statements).