Investments - Mortgage Loan Credit Monitoring (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator
Mortgage loans, Total amortized cost	$ 18,943.2	$ 18,103.9
Reinsurance recoverables	1,089.7	1,098.0
Accrued interest receivable	576.3	552.5
Commercial mortgage loans
Financing Receivable, Credit Quality Indicator
2021	666.7
2020	1,991.8	2,019.8
2019	2,775.1	2,769.9
2018	2,788.0	2,817.2
2017	1,998.3	2,049.3
2016		1,509.3
Prior	5,622.0	4,276.1
Mortgage loans, Total amortized cost	15,841.9	15,441.6
Accrued interest receivable	62.6	60.0
Commercial mortgage loans \| A- and above
Financing Receivable, Credit Quality Indicator
2021	621.3
2020	1,751.8	1,807.6
2019	2,481.3	2,486.8
2018	2,486.1	2,464.7
2017	1,729.8	1,780.8
2016		1,417.8
Prior	4,966.1	3,697.0
Mortgage loans, Total amortized cost	14,036.4	13,654.7
Commercial mortgage loans \| BBB+ thru BBB-
Financing Receivable, Credit Quality Indicator
2021	45.4
2020	197.8	149.1
2019	193.3	194.1
2018	301.9	352.5
2017	262.8	262.7
2016		75.8
Prior	561.6	499.7
Mortgage loans, Total amortized cost	1,562.8	1,533.9
Commercial mortgage loans \| BB+ thru BB-
Financing Receivable, Credit Quality Indicator
2020	29.2	23.7
2019	80.4	69.0
2016		9.1
Prior	52.4	43.9
Mortgage loans, Total amortized cost	162.0	145.7
Commercial mortgage loans \| B+ and below
Financing Receivable, Credit Quality Indicator
2020	13.0	39.4
2019	20.1	20.0
2017	5.7	5.8
2016		6.6
Prior	41.9	35.5
Mortgage loans, Total amortized cost	80.7	107.3
Direct financing leases
Financing Receivable, Credit Quality Indicator
2021	30.8
2020	187.8	209.7
2019	29.6	29.6
2018	66.1	65.8
2017	37.6	37.6
2016		19.3
Prior	367.1	348.8
Mortgage loans, Total amortized cost	719.0	710.8
Accrued interest receivable	1.6	0.5
Direct financing leases \| A- and above
Financing Receivable, Credit Quality Indicator
2020	43.9	43.9
2019	1.6	1.6
2018	42.7	42.6
2017	19.3	19.2
2016		15.3
Prior	217.3	202.9
Mortgage loans, Total amortized cost	324.8	325.5
Direct financing leases \| BBB+ thru BBB-
Financing Receivable, Credit Quality Indicator
2021	30.8
2020	88.1	94.9
2019	5.5	5.5
2018	11.4	11.3
2017	18.3	18.4
2016		3.0
Prior	38.8	35.5
Mortgage loans, Total amortized cost	192.9	168.6
Direct financing leases \| BB+ thru BB-
Financing Receivable, Credit Quality Indicator
2020	13.3	13.3
Prior	1.8	1.9
Mortgage loans, Total amortized cost	15.1	15.2
Direct financing leases \| B+ and below
Financing Receivable, Credit Quality Indicator
2020	42.5	57.6
2019	22.5	22.5
2018	12.0	11.9
2016		1.0
Prior	109.2	108.5
Mortgage loans, Total amortized cost	186.2	201.5
Residential mortgage loans
Financing Receivable, Credit Quality Indicator
2021	423.0
2020	713.6	699.1
2019	277.5	338.7
2018	147.7	167.8
2017	170.6	166.5
2016		168.0
Prior	649.9	411.4
Mortgage loans, Total amortized cost	2,382.3	1,951.5
Accrued interest receivable	6.0	2.0
Residential mortgage loans \| Performing
Financing Receivable, Credit Quality Indicator
2021	423.0
2020	713.0	699.1
2019	277.5	336.7
2018	147.7	167.0
2017	170.6	165.1
2016		167.6
Prior	641.4	398.7
Mortgage loans, Total amortized cost	2,373.2	1,934.2
Residential mortgage loans \| Non-performing
Financing Receivable, Credit Quality Indicator
2020	0.6
2019		2.0
2018		0.8
2017		1.4
2016		0.4
Prior	8.5	12.7
Mortgage loans, Total amortized cost	$ 9.1	$ 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

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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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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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- 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.

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