Investments - Components of Investment Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Net Investment Income [Line Items]
Investment income (loss)	$ 1,134.9	$ 584.1	$ 5,318.5	$ 72.4
Performance allocations - realized
Net Investment Income [Line Items]
Investment income (loss)	1,018.1	86.8	1,645.6	415.7
Performance allocations - unrealized
Net Investment Income [Line Items]
Investment income (loss)	(43.6)	390.6	3,195.7	315.9
Performance allocations
Net Investment Income [Line Items]
Investment income (loss)	974.5	477.4	4,841.3	731.6
Principal investment income (loss) from equity method investments (excluding performance allocations) - realized
Net Investment Income [Line Items]
Investment income (loss)	87.7	26.9	175.5	105.3
Principal investment income (loss) from equity method investments (excluding performance allocations) - unrealized
Net Investment Income [Line Items]
Investment income (loss)	30.5	48.8	239.4	(756.3)
Principal investment income (loss) from equity method investments (excluding performance allocations)
Net Investment Income [Line Items]
Investment income (loss)	118.2	75.7	414.9	(651.0)
Principal investment income (loss) from investments in CLOs and other investments - realized
Net Investment Income [Line Items]
Investment income (loss)	4.4	0.3	3.9	0.5
Principal investment income (loss) from investments in CLOs and other investments - unrealized
Net Investment Income [Line Items]
Investment income (loss)	37.8	30.7	58.4	(8.7)
Principal investment income (loss) from investments in CLOs and other investments - unrealized | Equity securities
Net Investment Income [Line Items]
Investment income (loss)	31.5		31.5
Principal investment income (loss) from investments in CLOs and other investments
Net Investment Income [Line Items]
Investment income (loss)	$ 42.2	$ 31.0	$ 62.3	$ (8.2)