Investments - Mortgage Loan Credit Monitoring (Details) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator
Mortgage loans, Total amortized cost	$ 19,153.6	$ 18,103.9
Reinsurance recoverables	1,093.4	1,098.0
Accrued interest receivable	544.9	552.5
Commercial mortgage loans
Financing Receivable, Credit Quality Indicator
2021	1,418.7
2020	2,036.5	2,019.8
2019	2,773.2	2,769.9
2018	2,679.9	2,817.2
2017	1,884.4	2,049.3
2016		1,509.3
Prior	5,368.8	4,276.1
Mortgage loans, Total amortized cost	16,161.5	15,441.6
Accrued interest receivable	62.0	60.0
Commercial mortgage loans \| A- and above
Financing Receivable, Credit Quality Indicator
2021	1,191.5
2020	1,741.5	1,807.6
2019	2,391.8	2,486.8
2018	2,471.2	2,464.7
2017	1,704.4	1,780.8
2016		1,417.8
Prior	4,764.4	3,697.0
Mortgage loans, Total amortized cost	14,264.8	13,654.7
Commercial mortgage loans \| BBB+ thru BBB-
Financing Receivable, Credit Quality Indicator
2021	218.8
2020	260.3	149.1
2019	331.0	194.1
2018	208.7	352.5
2017	180.0	262.7
2016		75.8
Prior	517.3	499.7
Mortgage loans, Total amortized cost	1,716.1	1,533.9
Commercial mortgage loans \| BB+ thru BB-
Financing Receivable, Credit Quality Indicator
2021	8.4
2020	34.7	23.7
2019	50.4	69.0
2016		9.1
Prior	51.9	43.9
Mortgage loans, Total amortized cost	145.4	145.7
Commercial mortgage loans \| B+ and below
Financing Receivable, Credit Quality Indicator
2020		39.4
2019		20.0
2017		5.8
2016		6.6
Prior	35.2	35.5
Mortgage loans, Total amortized cost	35.2	107.3
Direct financing leases
Financing Receivable, Credit Quality Indicator
2021	42.5
2020	173.5	209.7
2019	28.9	29.6
2018	64.9	65.8
2017	36.8	37.6
2016		19.3
Prior	347.4	348.8
Mortgage loans, Total amortized cost	694.0	710.8
Accrued interest receivable	1.9	0.5
Direct financing leases \| A- and above
Financing Receivable, Credit Quality Indicator
2020	92.4	43.9
2019	1.6	1.6
2018	44.7	42.6
2017	18.6	19.2
2016		15.3
Prior	286.0	202.9
Mortgage loans, Total amortized cost	443.3	325.5
Direct financing leases \| BBB+ thru BBB-
Financing Receivable, Credit Quality Indicator
2021	27.9
2020	62.5	94.9
2019	25.2	5.5
2018	20.2	11.3
2017	17.9	18.4
2016		3.0
Prior	59.0	35.5
Mortgage loans, Total amortized cost	212.7	168.6
Direct financing leases \| BB+ thru BB-
Financing Receivable, Credit Quality Indicator
2021	14.6
2020	16.9	13.3
2019	2.1
Prior	2.4	1.9
Mortgage loans, Total amortized cost	36.0	15.2
Direct financing leases \| B+ and below
Financing Receivable, Credit Quality Indicator
2020	1.7	57.6
2019		22.5
2018		11.9
2017	0.3
2016		1.0
Prior		108.5
Mortgage loans, Total amortized cost	2.0	201.5
Residential mortgage loans
Financing Receivable, Credit Quality Indicator
2021	574.8
2020	670.1	699.1
2019	230.5	338.7
2018	125.1	167.8
2017	143.3	166.5
2016		168.0
Prior	554.3	411.4
Mortgage loans, Total amortized cost	2,298.1	1,951.5
Accrued interest receivable	15.2	2.0
Residential mortgage loans \| Performing
Financing Receivable, Credit Quality Indicator
2021	574.8
2020	670.1	699.1
2019	229.8	336.7
2018	125.1	167.0
2017	143.3	165.1
2016		167.6
Prior	549.3	398.7
Mortgage loans, Total amortized cost	2,292.4	1,934.2
Residential mortgage loans \| Non-performing
Financing Receivable, Credit Quality Indicator
2019	0.7	2.0
2018		0.8
2017		1.4
2016		0.4
Prior	5.0	12.7
Mortgage loans, Total amortized cost	$ 5.7	$ 17.3
Mortgage loans, Days delinquent to be considered non-performing	90 days

The numbers of days for which a mortgage loan has been delinquent such that it is considered non-performing.

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Amount of financing receivable originated five years prior to current fiscal year.

+ References

No definition available.

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Amount of financing receivable originated more than five years prior to current fiscal year.

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Amount of financing receivable originated four years prior to current fiscal year.

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Amount of financing receivable originated in current fiscal year.

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Amount of financing receivable originated in fiscal year prior to current fiscal year.

+ References

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- Definition

Amount of financing receivable originated three years prior to current fiscal year.

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Amount of financing receivable originated two years prior to current fiscal year.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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- Definition

Carrying amount as of the balance sheet date of interest earned but not received. Also called accrued interest or accrued interest receivable.

+ References

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- Definition

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

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- Definition

Amount before valuation allowance recoverable under reinsurance contracts. Examples include, but are not limited to, settled and unsettled claims, incurred but not reported losses, loss adjustment expense, premium paid, policy benefits and policy reserves.

+ References

No definition available.

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