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Income Taxes - Effective Rate Reconciliation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Tax (expense) benefit at the U.S. statutory rate	$ (118.7)	$ 31.4	$ 57.5
Differences in taxes resulting from:
Non-U.S. earnings, net of foreign taxes	103.7	(41.2)	(78.2)
Bermuda corporate income tax	68.0	0.0	0.0
Change in valuation allowance	(30.2)	(19.6)	(2.0)
State taxes	(8.2)	(2.8)	(7.3)
Noncontrolling interest	6.8	3.4	2.1
Member’s surplus contributions	(5.7)	(6.2)	(5.6)
Withholding tax	(4.1)	(3.1)	(0.3)
Tax rate changes	(0.6)	(0.4)	(10.9)
Officer compensation	(0.2)	(1.0)	(1.5)
Tax exempt interest and dividends	0.2	0.2	0.2
Other, net	4.5	(2.1)	1.6
Total income tax (expense) benefit	$ 15.5	$ (41.4)	$ (44.4)

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