Investments - Net Investment Earnings (Loss) (Details) - NGP Management - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Schedule of Equity Method Investments [Line Items]
Management fee related revenues from NGP Management	$ 19.2	$ 19.8	$ 36.5	$ 37.9
Expenses related to the investment in NGP Management	(3.8)	(4.1)	(7.0)	(7.5)
Net investment income from NGP Management	$ 15.4	$ 15.7	$ 29.5	$ 30.4