Earnings per Common Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Earnings per Common Share [Abstract]
Net income	$ 106.9	$ 33.8
Less: Net income attributable to noncontrolling interests	87.3	20.4
Net income attributable to common shareholders	$ 19.6	$ 13.4
Weighted average shares outstanding - basic (in shares)	42.0	41.6
Net income available per common share - basic (in dollars per share)	$ 0.47	$ 0.32
Weighted average shares outstanding (in shares)	42.0	41.6
Dilutive effect of unvested stock awards (in shares)	0.1	0.4
Weighted average shares outstanding - diluted (in shares)	42.1	42.0
Net income available per common share - diluted (in dollars per share)	$ 0.47	$ 0.32