Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Numerator:
Income from continuing operations	$ (9.5)	$ 103.6	$ 174.3	$ 237.9
Less: dividends declared - common stock outstanding, restricted shares and restricted share units	(22.8)	(19.6)	(61.8)	(52.7)
Undistributed earnings	$ (32.3)	$ 84.0	$ 112.5	$ 185.2
Percent allocated to common shareholders	99.30%	99.50%	99.30%	99.50%
Undistributed earnings allocated to common shareholders	$ (32.1)	$ 83.6	$ 111.7	$ 184.3
Add: dividends declared - common stock	22.6	19.5	61.1	52.0
(Loss) income from continuing operations attributable to common shares	$ (9.5)	$ 103.1	$ 172.8	$ 236.3
Denominator (in thousands):
Denominator for basic EPS: weighted-average common shares outstanding	64,353,000	64,970,000	64,206,000	64,952,000
Effect of dilutive securities:
Performance awards (in shares)		348,000	252,000	348,000
Stock options (in shares)		669,000	421,000	752,000
Denominator for diluted EPS: adjusted weighted-average common shares outstanding and assumed conversion	64,353,000	65,987,000	64,879,000	66,052,000
Per share income from continuing operations:
Basic (in dollars per share)	$ (0.15)	$ 1.59	$ 2.69	$ 3.64
Diluted (in dollars per share)	$ (0.15)	$ 1.56	$ 2.66	$ 3.58
Basic weighted-average common shares outstanding	64,353,000	64,970,000	64,206,000	64,952,000
Basic weighted-average common shares outstanding, unvested restricted shares expected to vest and restricted share units	64,809,000	65,304,000	64,662,000	65,286,000
Percent allocated to common shareholders	99.30%	99.50%	99.30%	99.50%
Income (loss) from discontinued operations and net income
Income (loss) from discontinued operations attributable to common shareholders for basic and diluted earnings per share	$ (0.3)		$ (0.4)
Net income attributable to common shareholders for basic and diluted earnings per share	$ (9.8)	$ 103.1	$ 172.4	$ 236.3
Antidilutive stock options excluded from EPS calculation (in shares)	1,000		125,000
Performance share awards
Income (loss) from discontinued operations and net income
Antidilutive stock options excluded from EPS calculation (in shares)	252,000
Stock options
Income (loss) from discontinued operations and net income
Antidilutive stock options excluded from EPS calculation (in shares)	326,000