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Investments - Financing Receivable, Non-Accrual and Aging (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2022	Jun. 30, 2022	Dec. 31, 2021	Dec. 31, 2020
Financing receivables, non-accrual and aging disclosures
Financing receivables, Non-accrual status	$ 55.0	$ 55.0	$ 17.2	$ 21.5
Financing receivables, Non-accrual assets without a valuation allowance	0.7	0.7	0.7
Financing receivables, Nonaccrual, Interest Income	0.5	0.8
Financing receivables, Total amortized cost	20,924.4	20,924.4	20,324.5
Recorded investment 90 days or more past due and accruing	6.9	6.9	5.3
Reinsurance recoverable and deposit receivable	23,603.7	23,603.7	1,189.3
Current
Financing receivables, non-accrual and aging disclosures
Financing receivables, Total amortized cost	20,809.2	20,809.2	20,240.1
Past Due
Financing receivables, non-accrual and aging disclosures
Financing receivables, Total amortized cost	115.2	115.2	84.4
Reinsurance recoverable and deposit receivable	0.0	0.0	0.0
30 to 59 Days Past Due
Financing receivables, non-accrual and aging disclosures
Financing receivables, Total amortized cost	77.8	77.8	59.9
60 to 89 Days Past Due
Financing receivables, non-accrual and aging disclosures
Financing receivables, Total amortized cost	11.0	11.0	11.5
90 Days or More Past Due
Financing receivables, non-accrual and aging disclosures
Financing receivables, Total amortized cost	26.4	26.4	13.0
Commercial mortgage loans
Financing receivables, non-accrual and aging disclosures
Financing receivables, Non-accrual status	49.7	49.7	13.2	10.7
Financing receivables, Nonaccrual, Interest Income	0.5	0.8
Financing receivables, Total amortized cost	16,607.9	16,607.9	16,394.7
Recorded investment 90 days or more past due and accruing			2.7
Commercial mortgage loans \| Current
Financing receivables, non-accrual and aging disclosures
Financing receivables, Total amortized cost	16,580.4	16,580.4	16,386.9
Commercial mortgage loans \| Past Due
Financing receivables, non-accrual and aging disclosures
Financing receivables, Total amortized cost	27.5	27.5	7.8
Commercial mortgage loans \| 30 to 59 Days Past Due
Financing receivables, non-accrual and aging disclosures
Financing receivables, Total amortized cost	11.5	11.5	0.7
Commercial mortgage loans \| 60 to 89 Days Past Due
Financing receivables, non-accrual and aging disclosures
Financing receivables, Total amortized cost	0.7	0.7
Commercial mortgage loans \| 90 Days or More Past Due
Financing receivables, non-accrual and aging disclosures
Financing receivables, Total amortized cost	15.3	15.3	7.1
Direct financing leases
Financing receivables, non-accrual and aging disclosures
Financing receivables, Total amortized cost	581.9	581.9	609.9
Recorded investment 90 days or more past due and accruing			0.7
Direct financing leases \| Current
Financing receivables, non-accrual and aging disclosures
Financing receivables, Total amortized cost	569.4	569.4	607.3
Direct financing leases \| Past Due
Financing receivables, non-accrual and aging disclosures
Financing receivables, Total amortized cost	12.5	12.5	2.6
Direct financing leases \| 30 to 59 Days Past Due
Financing receivables, non-accrual and aging disclosures
Financing receivables, Total amortized cost	10.8	10.8
Direct financing leases \| 60 to 89 Days Past Due
Financing receivables, non-accrual and aging disclosures
Financing receivables, Total amortized cost	1.7	1.7	1.9
Direct financing leases \| 90 Days or More Past Due
Financing receivables, non-accrual and aging disclosures
Financing receivables, Total amortized cost			0.7
Residential mortgage loans
Financing receivables, non-accrual and aging disclosures
Financing receivables, Non-accrual status	5.3	5.3	4.0	$ 10.8
Financing receivables, Non-accrual assets without a valuation allowance	0.7	0.7	0.7
Financing receivables, Total amortized cost	3,734.6	3,734.6	3,319.9
Recorded investment 90 days or more past due and accruing	6.9	6.9	1.9
Residential mortgage loans \| Current
Financing receivables, non-accrual and aging disclosures
Financing receivables, Total amortized cost	3,659.4	3,659.4	3,245.9
Residential mortgage loans \| Past Due
Financing receivables, non-accrual and aging disclosures
Financing receivables, Total amortized cost	75.2	75.2	74.0
Residential mortgage loans \| 30 to 59 Days Past Due
Financing receivables, non-accrual and aging disclosures
Financing receivables, Total amortized cost	55.5	55.5	59.2
Residential mortgage loans \| 60 to 89 Days Past Due
Financing receivables, non-accrual and aging disclosures
Financing receivables, Total amortized cost	8.6	8.6	9.6
Residential mortgage loans \| 90 Days or More Past Due
Financing receivables, non-accrual and aging disclosures
Financing receivables, Total amortized cost	$ 11.1	$ 11.1	$ 5.2