Investments - Schedule of Net Investment Earnings (Loss) from NGP (Details) - NGP Management Company LLC - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Management fee-related revenues from NGP Management	$ 72.9	$ 73.9	$ 97.8
Expenses related to the investment in NGP Management	(10.8)	(11.0)	(10.5)
Amortization of basis differences from the investment in NGP Management	(2.9)	(4.3)	(5.7)
Net investment income from NGP Management	$ 59.2	$ 58.6	$ 81.6