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Investments - Investments in NGP (Details) - USD ($)
$ in Millions
Sep. 30, 2023
Dec. 31, 2022
Schedule of Equity Method Investments [Line Items]    
Total $ 3,008.3 $ 2,922.0
Investment in NGP Management    
Schedule of Equity Method Investments [Line Items]    
Total 372.9 369.7
Investments in NGP general partners - accrued performance allocations    
Schedule of Equity Method Investments [Line Items]    
Total 516.3 564.5
Principal investments in NGP funds    
Schedule of Equity Method Investments [Line Items]    
Total $ 65.4 $ 81.5