Borrowings - Schedule of Debt Obligations (Details) - USD ($) $ in Millions	Sep. 30, 2026	Dec. 31, 2025	May 31, 2021
Debt Instrument [Line Items]
Borrowing Outstanding	$ 3,045.4	$ 3,025.1
Carrying Value	3,016.7	2,997.0
CLO Borrowings
Debt Instrument [Line Items]
Borrowing Outstanding	370.4	350.1
Carrying Value	$ 367.7	349.4
3.500% Senior Notes Due 9/19/2029
Debt Instrument [Line Items]
Interest rate (percent)	3.50%
Borrowing Outstanding	$ 425.0	425.0
Carrying Value	$ 423.7	423.4
5.050% Senior Notes Due 9/19/2035
Debt Instrument [Line Items]
Interest rate (percent)	5.05%
Borrowing Outstanding	$ 800.0	800.0
Carrying Value	$ 791.8	791.1
5.625% Senior Notes Due 3/30/2043
Debt Instrument [Line Items]
Interest rate (percent)	5.625%
Borrowing Outstanding	$ 600.0	600.0
Carrying Value	$ 600.5	600.5
5.650% Senior Notes Due 9/15/2048
Debt Instrument [Line Items]
Interest rate (percent)	5.65%
Borrowing Outstanding	$ 350.0	350.0
Carrying Value	$ 346.8	346.7
4.625% Subordinated Notes Due 5/15/2061
Debt Instrument [Line Items]
Interest rate (percent)	4.625%		4.625%
Borrowing Outstanding	$ 500.0	500.0
Carrying Value	$ 486.2	$ 485.9