Earnings Per Share - Schedule of Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Basic earnings per share
Net income from continuing operations	$ 64.9	$ 73.0	$ 190.2	$ 179.0
Amount allocated to nonvested participating shareholders	(0.2)	(0.2)	(0.6)	(0.6)
Income before discontinued operations available to common shareholders - Basic	64.7	72.8	189.6	178.4
Loss from discontinued operations, net	(11.7)	(61.9)	(67.2)	(59.4)
Amount allocated to nonvested participating shareholders	0.0	0.0	0.0	0.0
Loss from discontinued operations available to common shareholders - Basic	(11.7)	(61.9)	(67.2)	(59.4)
Net income	53.2	11.1	123.0	119.6
Amount allocated to nonvested participating shareholders	(0.2)	(0.2)	(0.6)	(0.6)
Net income available to common shareholders - Basic	$ 53.0	$ 10.9	$ 122.4	$ 119.0
Average common shares outstanding - Basic	233.2	227.8	233.0	220.3
Earnings per share from continuing operations available to common shareholders - Basic	$ 0.28	$ 0.32	$ 0.81	$ 0.81
Earnings per share from discontinued operations available to common shareholders - Basic	(0.05)	(0.28)	(0.28)	(0.27)
Earnings per share - Basic	$ 0.23	$ 0.04	$ 0.53	$ 0.54
Diluted earnings per share
Net income from continuing operations	$ 64.9	$ 73.0	$ 190.2	$ 179.0
Amount allocated to nonvested participating shareholders	(0.2)	(0.2)	(0.6)	(0.6)
Income before discontinued operations available to common shareholders - Diluted	64.7	72.8	189.6	178.4
Loss from discontinued operations, net	(11.7)	(61.9)	(67.2)	(59.4)
Amount allocated to nonvested participating shareholders	0.0	0.0	0.0	0.0
Loss from discontinued operations available to common shareholders - Diluted	(11.7)	(61.9)	(67.2)	(59.4)
Net income	53.2	11.1	123.0	119.6
Amount allocated to nonvested participating shareholders	(0.2)	(0.2)	(0.6)	(0.6)
Net income available to common shareholders - Diluted	$ 53.0	$ 10.9	$ 122.4	$ 119.0
Average common shares outstanding - Basic	233.2	227.8	233.0	220.3
Assumed conversion of stock options, unvested restricted stock and contingent performance shares, net	1.5	0.5	1.4	0.5
Average common shares outstanding - Diluted	234.7	228.3	234.4	220.8
Earnings per share from continuing operations available to common shareholders - Diluted	$ 0.28	$ 0.32	$ 0.81	$ 0.81
Earnings per share from discontinued operations available to common shareholders - Diluted	(0.05)	(0.28)	(0.28)	(0.27)
Earnings per share - Diluted	$ 0.23	$ 0.04	$ 0.53	$ 0.54
Anti-dilutive shares	0.0	0.0	0.0	0.0