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Commitments and Contingent Liabilities (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Jul. 31, 2017
Commitments and Contingent Liabilities [Line Items]
Litigation and regulatory matters loss contingency, range of possible loss, maximum (less than)	$ 100.0		$ 100.0
Indonesia \| CT Corp Joint Venture
Commitments and Contingent Liabilities [Line Items]
Joint Venture with CT Corp, Ownership Percentage						49.00%
Commitments \| Commercial mortgage loans
Commitments and Contingent Liabilities [Line Items]
Total outstanding mortgage loan commitments	506.0		506.0		$ 333.0
Allowance for credit losses	0.0		0.0		0.1
Change in allowance for credit loss expense (reversal)	0.1	$ 0.0	0.0	$ 0.0
Commitments \| Investments
Commitments and Contingent Liabilities [Line Items]
Commitments to purchase investment (excluding commercial mortgage loans)	1,279.0		1,279.0		582.0
Purchase Commitment
Commitments and Contingent Liabilities [Line Items]
Change in allowance for credit loss expense (reversal)	0.0	$ 0.0	0.0	$ 0.0
Other Guarantees
Commitments and Contingent Liabilities [Line Items]
Accrued liabilities	$ 32.0		$ 32.0		$ 33.0