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Debt - Senior Notes and Junior Subordinated Notes (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Mar. 31, 2024	Sep. 30, 2024	Sep. 30, 2023	Aug. 20, 2024	Mar. 20, 2024
Debt Instrument [Line Items]
Repayments of long-term debt		$ 750.0	$ 25.0
Junior subordinated notes | On or after March 30, 2029
Debt Instrument [Line Items]
Redemption price percentage		100.00%
Junior subordinated notes | If changes in tax laws and interpretations occur
Debt Instrument [Line Items]
Redemption price percentage		100.00%
Junior subordinated notes | If a rating agency makes certain changes relating to the equity credit criteria for securities
Debt Instrument [Line Items]
Redemption price percentage		102.00%
4.25% senior notes | Senior notes
Debt Instrument [Line Items]
Repayments of long-term debt	$ 400.0
Debt interest rate	4.25%
2034 Senior Notes | Senior notes
Debt Instrument [Line Items]
Debt interest rate		5.50%
Face amount		$ 400.0		$ 400.0
Redemption price percentage		100.00%
2025 Senior Notes | Senior notes
Debt Instrument [Line Items]
Debt interest rate		3.50%
Face amount		$ 350.0
Redemption price percentage		100.00%
Applicable basis spread over redemption price percentage		0.25%
2030 Senior Notes | Senior notes
Debt Instrument [Line Items]
Debt interest rate		3.30%
Face amount		$ 350.0
Redemption price percentage		100.00%
Applicable basis spread over redemption price percentage		0.40%
6.750% Junior Subordinated Notes due 2064 | Junior subordinated notes
Debt Instrument [Line Items]
Debt interest rate		6.75%
Face amount		$ 450.0			$ 450.0
6.750% Junior Subordinated Notes due 2064 | Junior subordinated notes | On or after March 30, 2029
Debt Instrument [Line Items]
Redemption price percentage		100.00%

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