Affiliate Equity - Changes in the Company's Interest in its Affiliates on the Controlling Interest's Equity (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Affiliate Equity [Abstract]
Net income (loss) (controlling interest)	$ 107.7	$ 117.0	$ (93.1)	$ 270.0
Decrease in controlling interest paid-in capital from Affiliate equity issuances	(0.2)	(2.3)	(0.9)	(3.3)
Increase / (decrease) in controlling interest paid-in capital from Affiliate equity repurchases	(13.3)	1.0	(30.6)	(32.1)
Net income (loss) (controlling interest) including the net impact of Affiliate equity transactions	$ 94.2	$ 115.7	$ (124.6)	$ 234.6

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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