Income Taxes - Summary of Tax Effects of Temporary Differences (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets
Federal foreign tax credit carryforward	$ 46.8	$ 37.3
State net operating loss carryforwards	5.7	5.9
Tax basis goodwill and intangibles	240.3	259.8
Depreciation and amortization	61.7	25.4
Deferred restricted common unit compensation	36.5	24.7
Lease liabilities	116.1	119.0
Accrued compensation	926.2	781.3
Other	109.8	140.4
Deferred tax assets before valuation allowance	1,543.1	1,393.8
Valuation allowance	(62.8)	(56.7)
Total deferred tax assets	1,480.3	1,337.1
Deferred tax liabilities
Unrealized appreciation on investments	1,333.8	1,558.0
Lease right-of-use assets	87.7	89.2
Basis difference in investments	48.8	47.9
Other	38.8	28.9
Total deferred tax liabilities	1,509.1	1,724.0
Net deferred tax assets (liabilities)	(28.8)	(386.9)
Amount of deferred tax liabilities offset for presentation purposes	$ 1,463.8	$ 1,321.3