Earnings Per Share (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Numerator
Net income (controlling interest)	$ 75.2	$ 54.9	$ 202.3	$ 98.9
Convertible securities interest expense, net	2.6	0	0	0
Net income (controlling interest), as adjusted	$ 77.8	$ 54.9	$ 202.3	$ 98.9
Denominator
Average shares outstanding - basic (in shares)	53.2	51.7	53.0	51.6
Effect of dilutive instruments:
Contingently convertible securities (in shares)	2.0	0	0	0
Stock options and restricted stock (in shares)	1.3	1.3	1.4	1.3
Forward equity sales (in shares)	0.4	0	0.3	0
Average shares outstanding—diluted (in shares)	56.9	53.0	54.7	52.9
Stock options and other awards [Member]
Anti-dilutive securities
Anti-dilutive securities excluded from computation of diluted earnings per share (in shares)	0	0.6	0	0.6
Senior convertible securities [Member]
Anti-dilutive securities
Anti-dilutive securities excluded from computation of diluted earnings per share (in shares)	1.3	3.7	2.9	3.7
Junior convertible trust preferred securities [Member]
Anti-dilutive securities
Anti-dilutive securities excluded from computation of diluted earnings per share (in shares)	2.2	4.2	4.2	4.2
Forward equity sales [Member]
Anti-dilutive securities
Anti-dilutive securities excluded from computation of diluted earnings per share (in shares)	0	0.3	0	0.3