Investments - Components of Investment Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Schedule of Investments [Line Items]
Unrealized principal investment (income) loss	$ 44.8	$ 1,898.0	$ 6,721.9
Performance allocations - realized
Schedule of Investments [Line Items]
Unrealized principal investment (income) loss	867.0	2,048.8	2,956.7
Performance allocations - unrealized
Schedule of Investments [Line Items]
Unrealized principal investment (income) loss	(955.6)	(721.3)	3,127.9
Performance allocations
Schedule of Investments [Line Items]
Unrealized principal investment (income) loss	(88.6)	1,327.5	6,084.6
Principal investment income (loss) from equity method investments - realized
Schedule of Investments [Line Items]
Unrealized principal investment (income) loss	231.7	73.1	266.2
Principal investment income (loss) from equity method investments - unrealized
Schedule of Investments [Line Items]
Unrealized principal investment (income) loss	(115.1)	546.4	290.8
Principal investment income (loss) from equity method investments
Schedule of Investments [Line Items]
Unrealized principal investment (income) loss	116.6	619.5	557.0
Principal investment income (loss) from investments in CLOs and other investments - realized
Schedule of Investments [Line Items]
Unrealized principal investment (income) loss	(1.1)	5.0	1.9
Principal investment income (loss) from investments in CLOs and other investments- unrealized
Schedule of Investments [Line Items]
Unrealized principal investment (income) loss	17.9	(54.0)	78.4
Principal investment income (loss) from investments in CLOs and other investments- unrealized | Corporate investment
Schedule of Investments [Line Items]
Unrealized principal investment (income) loss	(13.3)		49.8
Principal investment income (loss) from investments in CLOs and other investments
Schedule of Investments [Line Items]
Unrealized principal investment (income) loss	$ 16.8	$ (49.0)	$ 80.3