Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Numerator:
Income from continuing operations	$ 86.4	$ (9.5)	$ 250.2	$ 174.3
Less: dividends declared - common stock outstanding, restricted shares and restricted share units	(23.2)	(22.8)	(69.0)	(61.8)
Undistributed earnings	$ 63.2	$ (32.3)	$ 181.2	$ 112.5
Percent allocated to common shareholders	99.30%	99.30%	99.40%	99.30%
Undistributed earnings available to common shareholders	$ 62.8	$ (32.1)	$ 180.1	$ 111.7
Add: dividends declared - common stock	23.2	22.6	68.1	61.1
Income (loss) from continuing operations attributable to common shares	$ 86.0	$ (9.5)	$ 248.2	$ 172.8
Denominator (in thousands):
Denominator for basic EPS: weighted-average common shares outstanding	62,432	64,353	63,503	64,206
Effect of dilutive securities:
Performance awards (in shares)	82	0	82	252
Stock options (in shares)	283	0	331	421
Denominator for diluted EPS: adjusted weighted-average common shares outstanding and assumed conversion	62,797	64,353	63,916	64,879
Per share income from continuing operations attributable to common shares:
Basic (in dollars per share)	$ 1.38	$ (0.15)	$ 3.91	$ 2.69
Diluted (in dollars per share)	$ 1.37	$ (0.15)	$ 3.89	$ 2.66
Basic weighted-average common shares outstanding	62,432	64,353	63,503	64,206
Basic weighted-average common shares outstanding, unvested restricted shares expected to vest and restricted share units	62,846	64,809	63,918	64,662
Percent allocated to common shareholders	99.30%	99.30%	99.40%	99.30%
Income (loss) from discontinued operations and net income
(Loss) income from discontinued operations attributable to common shareholders for basic and diluted earnings per share	$ (0.1)	$ (0.3)	$ 0.2	$ (0.4)
Net income attributable to common shareholders for basic and diluted earnings per share	$ 85.9	$ (9.8)	$ 248.4	$ 172.4
Antidilutive stock options excluded from EPS calculation (in shares)	377	1	328	125
Performance shares
Income (loss) from discontinued operations and net income
Antidilutive stock options excluded from EPS calculation (in shares)		252
Stock options
Income (loss) from discontinued operations and net income
Antidilutive stock options excluded from EPS calculation (in shares)		326