Earnings Per Share - Schedule of Earnings Per Share (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Basic earnings per share
Net income from continuing operations	$ 58.4	$ 51.6	$ 105.4	$ 92.8
Amount allocated to nonvested participating shareholders	(0.2)	(0.2)	(0.4)	(0.3)
Income before discontinued operations available to common shareholders - Basic	58.2	51.4	105.0	92.5
Income (Loss) from discontinued operations, net	0	(0.2)	3.1	0.1
Amount allocated to nonvested participating shareholders	0	0	0	0
Income (Loss) from discontinued operations available to common shareholders - Basic	0	(0.2)	3.1	0.1
Net income	58.4	51.4	108.5	92.9
Amount allocated to nonvested participating shareholders	(0.2)	(0.2)	(0.4)	(0.3)
Net income available to common shareholders - Basic	58.2	51.2	108.1	92.6
Average common shares outstanding - Basic	215.4	215.0	215.3	214.8
Earnings per share from continuing operations available to common shareholders - Basic	$ 0.27	$ 0.24	$ 0.49	$ 0.43
Earnings per share from discontinued operations available to common shareholders - Basic	$ 0.00	$ 0.00	$ 0.01	$ 0.00
Earnings per share - Basic	$ 0.27	$ 0.24	$ 0.50	$ 0.43
Diluted earnings per share
Net income from continuing operations	58.4	51.6	105.4	92.8
Amount allocated to nonvested participating shareholders	(0.2)	(0.2)	(0.4)	(0.3)
Income before discontinued operations available to common shareholders - Diluted	58.2	51.4	105.0	92.5
Income (Loss) from discontinued operations, net	0	(0.2)	3.1	0.1
Amount allocated to nonvested participating shareholders	0	0	0	0
Income (Loss) from discontinued operations available to common shareholders - Diluted	0	(0.2)	3.1	0.1
Net income	58.4	51.4	108.5	92.9
Amount allocated to nonvested participating shareholders	(0.2)	(0.2)	(0.4)	(0.3)
Net income available to common shareholders - Diluted	$ 58.2	$ 51.2	$ 108.1	$ 92.6
Unadjusted average common shares outstanding - Diluted	215.4	215.0	215.3	214.8
Assumed conversion of stock options, unvested restricted stock and contingent performance shares, net	0.5	0.5	0.5	0.5
Average common shares outstanding - Diluted	215.9	215.5	215.8	215.3
Earnings per share from continuing operations available to common shareholders - Diluted	$ 0.27	$ 0.24	$ 0.49	$ 0.43
Earnings per share from discontinued operations available to common shareholders - Diluted	$ 0.00	$ 0.00	$ 0.01	$ 0.00
Earnings per share - Diluted	$ 0.27	$ 0.24	$ 0.50	$ 0.43
Anti-dilutive shares	0	0	0	0