Investments - Schedule of Summarized Financial Information, Equity Fund (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Investments in Unconsolidated Affiliates
Total assets	$ 3,788.6	$ 1,852.2	$ 3,788.6	$ 1,852.2	$ 2,092.2
Total liabilities	654.8		654.8		562.4
Equity in Losses of Unconsolidated Affiliates
Total net investment loss	586.4	$ 76.5	1,503.7	$ 89.1
Equity Fund | Unconsolidated affiliates
Investments in Unconsolidated Affiliates
Due from brokers and counterparties	290.7		290.7		138.4
Investments, at fair value	146.3		146.3		0.0
Derivative contracts, at fair value	91.3		91.3		2.4
Total assets	528.3		528.3		140.8
Capital received in advance	25.8		25.8		45.2
Other liabilities	0.6		0.6		0.2
Total liabilities	26.4		26.4		45.4
Net assets	501.9		501.9		$ 95.4
Equity in Losses of Unconsolidated Affiliates
Total net investment loss	(0.8)		(1.1)
Realized gain on securities and derivative contracts	85.5		86.0
Change in unrealized gain on securities and derivative contracts	212.1		91.6
Change in net assets from operations	$ 296.8		$ 176.5