Investments - Mortgage Loan Credit Monitoring (Details) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2022	Dec. 31, 2021
Financing Receivable, Credit Quality Indicator
Mortgage loans, Total amortized cost	$ 20,924.4	$ 20,324.5
Reinsurance recoverable and deposit receivable	23,603.7	1,189.3
Accrued interest receivable	553.8	542.6
Commercial mortgage loans
Financing Receivable, Credit Quality Indicator
2022	957.9
2021	2,678.2	2,587.3
2020	1,999.1	2,033.6
2019	2,635.5	2,706.9
2018	2,473.3	2,523.5
2017		1,739.3
Prior	5,863.9	4,804.1
Mortgage loans, Total amortized cost	16,607.9	16,394.7
Accrued interest receivable	55.1	60.7
Commercial mortgage loans \| A- and above
Financing Receivable, Credit Quality Indicator
2022	918.5
2021	2,285.2	2,275.9
2020	1,787.5	1,722.7
2019	2,369.2	2,412.9
2018	2,265.1	2,383.3
2017		1,437.2
Prior	5,211.7	4,334.2
Mortgage loans, Total amortized cost	14,837.2	14,566.2
Commercial mortgage loans \| BBB+ thru BBB-
Financing Receivable, Credit Quality Indicator
2022	39.4
2021	345.8	278.6
2020	206.5	305.6
2019	266.3	294.0
2018	199.6	131.4
2017		302.1
Prior	569.0	380.0
Mortgage loans, Total amortized cost	1,626.6	1,691.7
Commercial mortgage loans \| BB+ thru BB-
Financing Receivable, Credit Quality Indicator
2021	47.2	32.8
2020	5.1	5.3
Prior	44.6	55.4
Mortgage loans, Total amortized cost	96.9	93.5
Commercial mortgage loans \| B+ and below
Financing Receivable, Credit Quality Indicator
2018	8.6	8.8
Prior	38.6	34.5
Mortgage loans, Total amortized cost	47.2	43.3
Direct financing leases
Financing Receivable, Credit Quality Indicator
2022	114.3
2021	80.9	94.2
2020	108.0	113.1
2019	13.4	25.3
2018	47.7	57.3
2017		32.1
Prior	217.6	287.9
Mortgage loans, Total amortized cost	581.9	609.9
Accrued interest receivable	1.0	1.2
Direct financing leases \| A- and above
Financing Receivable, Credit Quality Indicator
2022	89.9
2021	11.3	11.7
2020	39.9	41.8
2019	1.3	1.4
2018	37.6	39.4
2017		16.6
Prior	153.3	235.6
Mortgage loans, Total amortized cost	333.3	346.5
Direct financing leases \| BBB+ thru BBB-
Financing Receivable, Credit Quality Indicator
2022	24.4
2021	19.0	30.2
2020	55.3	57.9
2019	10.4	22.0
2018	10.1	17.9
2017		15.5
Prior	62.4	50.2
Mortgage loans, Total amortized cost	181.6	193.7
Direct financing leases \| BB+ thru BB-
Financing Receivable, Credit Quality Indicator
2021	49.3	50.8
2020	12.8	13.4
2019	1.7	1.9
Prior	1.9	2.1
Mortgage loans, Total amortized cost	65.7	68.2
Direct financing leases \| B+ and below
Financing Receivable, Credit Quality Indicator
2021	1.3	1.5
Mortgage loans, Total amortized cost	1.3	1.5
Residential mortgage loans
Financing Receivable, Credit Quality Indicator
2022	521.7
2021	2,098.8	2,039.1
2020	458.4	511.9
2019	137.1	156.2
2018	75.6	91.2
2017		103.2
Prior	443.0	418.3
Mortgage loans, Total amortized cost	3,734.6	3,319.9
Accrued interest receivable	17.2	16.7
Residential mortgage loans \| Performing
Financing Receivable, Credit Quality Indicator
2022	521.7
2021	2,096.1	2,039.1
2020	455.8	510.1
2019	136.1	155.6
2018	74.0	91.2
2017		102.4
Prior	438.7	415.6
Mortgage loans, Total amortized cost	3,722.4	3,314.0
Residential mortgage loans \| Non-performing
Financing Receivable, Credit Quality Indicator
2021	2.7
2020	2.6	1.8
2019	1.0	0.6
2018	1.6
2017		0.8
Prior	4.3	2.7
Mortgage loans, Total amortized cost	$ 12.2	$ 5.9
Mortgage loans, Days delinquent to be considered non-performing	90 days

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

+ References

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Amount excluding accrued interest, before allowance for credit loss, of financing receivable.

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

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

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

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Amount excluding accrued interest of financing receivable originated in current fiscal year.

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

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

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