Investments - Financing Receivable, Non-Accrual and Aging (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
Jun. 30, 2021	Dec. 31, 2020	Dec. 31, 2019
Financing receivables, non-accrual and aging disclosures
Financing receivables, Non-accrual status	$ 10.3	$ 21.5	$ 11.8
Financing receivables, Non-accrual assets without a valuation allowance	0.7	0.7
Financing receivables, Nonaccrual, Interest Income	0.0	0.0
Past due	110.2	152.8
Current	19,043.4	17,951.1
Financing receivables, Total amortized cost	19,153.6	18,103.9
Recorded investment 90 days or more past due and accruing	48.9	7.8
Reinsurance recoverables	0.0	0.0
30 to 59 Days Past Due
Financing receivables, non-accrual and aging disclosures
Past due	42.6	108.7
60 to 89 Days Past Due
Financing receivables, non-accrual and aging disclosures
Past due	9.6	21.2
90 Days or More Past Due
Financing receivables, non-accrual and aging disclosures
Past due	58.0	22.9
Commercial mortgage loans
Financing receivables, non-accrual and aging disclosures
Financing receivables, Non-accrual status	5.0	10.7	5.0
Past due	32.4	63.3
Current	16,129.1	15,378.3
Financing receivables, Total amortized cost	16,161.5	15,441.6
Recorded investment 90 days or more past due and accruing	3.0	1.3
Commercial mortgage loans \| 30 to 59 Days Past Due
Financing receivables, non-accrual and aging disclosures
Past due	18.7	42.1
Commercial mortgage loans \| 60 to 89 Days Past Due
Financing receivables, non-accrual and aging disclosures
Past due	5.6	9.2
Commercial mortgage loans \| 90 Days or More Past Due
Financing receivables, non-accrual and aging disclosures
Past due	8.1	12.0
Direct financing leases
Financing receivables, non-accrual and aging disclosures
Past due	47.2	3.2
Current	646.8	707.6
Financing receivables, Total amortized cost	694.0	710.8
Recorded investment 90 days or more past due and accruing	45.5
Direct financing leases \| 30 to 59 Days Past Due
Financing receivables, non-accrual and aging disclosures
Past due	1.7
Direct financing leases \| 60 to 89 Days Past Due
Financing receivables, non-accrual and aging disclosures
Past due		3.2
Direct financing leases \| 90 Days or More Past Due
Financing receivables, non-accrual and aging disclosures
Past due	45.5
Residential mortgage loans
Financing receivables, non-accrual and aging disclosures
Financing receivables, Non-accrual status	5.3	10.8	$ 6.8
Financing receivables, Non-accrual assets without a valuation allowance	0.7	0.7
Past due	30.6	86.3
Current	2,267.5	1,865.2
Financing receivables, Total amortized cost	2,298.1	1,951.5
Recorded investment 90 days or more past due and accruing	0.4	6.5
Residential mortgage loans \| 30 to 59 Days Past Due
Financing receivables, non-accrual and aging disclosures
Past due	22.2	66.6
Residential mortgage loans \| 60 to 89 Days Past Due
Financing receivables, non-accrual and aging disclosures
Past due	4.0	8.8
Residential mortgage loans \| 90 Days or More Past Due
Financing receivables, non-accrual and aging disclosures
Past due	$ 4.4	$ 10.9

Amount of interest income on financing receivable on nonaccrual status.

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Amount of financing receivable on nonaccrual status with no allowance for credit loss.

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Amount of financing receivable 90 days or more past due and still accruing.

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Amount of financing receivable not past due.

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Amount of financing receivable past due.

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Amount, before allowance for credit loss, of financing receivable.

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Amount of reinsurance recoverable past due.

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