Earnings Per Share (Details) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Numerator:
Income from continuing operations	$ 8.2	$ 89.4	$ 63.5	$ 149.4
Less: dividends declared - common stock outstanding, unvested restricted shares and restricted share units	(12.8)	(11.3)	(25.6)	(22.5)
Undistributed earnings	(4.6)	78.1	37.9	126.9
Percent allocated to common shareholders	99.50%	99.40%	99.50%	99.40%
Undistributed earnings allocated to common shareholders	(4.6)	77.6	37.7	126.2
Add: dividends declared - common stock	12.7	11.2	25.5	22.4
Numerator for basic and diluted EPS	8.1	88.8	63.2	148.6
Denominator (in thousands):
Denominator for basic EPS: weighted-average common shares outstanding	63,409	62,419	63,343	62,166
Effect of dilutive securities:
Performance awards (in shares)	353	505	353	505
Stock options (in shares)	933	873	924	812
Denominator for diluted EPS: adjusted weighted average common shares outstanding and assumed conversion	64,695	63,797	64,620	63,483
Per share income from continuing operations:
Basic (in dollars per share)	$ 0.13	$ 1.42	$ 1.00	$ 2.39
Diluted (in dollars per share)	$ 0.13	$ 1.39	$ 0.98	$ 2.34
Basic weighted-average common shares outstanding	63,409	62,419	63,343	62,166
Basic weighted-average common shares outstanding, unvested restricted shares expected to vest and restricted share units	63,737	62,783	63,670	62,529
Percent allocated to common shareholders	99.50%	99.40%	99.50%	99.40%
Income from discontinued operations and net income
Income from discontinued operations attributable to common shareholders for basic and diluted earnings per share		3.4	(0.1)	3.4
Net income attributable to common shareholders for basic and diluted earnings per share	$ 8.1	$ 92.2	$ 63.1	$ 151.9