Investments - Credit Quality Indicators (Details) - Commercial Portfolio Segment $ in Millions	Sep. 30, 2022 USD ($)	Dec. 31, 2021 USD ($)
Greater than 2.0
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated current year	$ 24.0	$ 59.3
Financing receivable, originated year one	57.9	5.6
Financing receivable, originated year two	2.7	0.0
Financing receivable, originated year three	0.0	0.0
Financing receivable, originated year four	0.0	0.0
Prior	56.8	70.5
Financing receivable, before allowance for credit loss	$ 141.4	$ 135.4
Percentage of financing receivable, before allowance for credit loss	0.463	0.526
1.5 to 2.0
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated current year	$ 26.9	$ 34.1
Financing receivable, originated year one	37.1	0.0
Financing receivable, originated year two	0.0	0.0
Financing receivable, originated year three	0.0	4.7
Financing receivable, originated year four	4.6	4.0
Prior	19.6	17.5
Financing receivable, before allowance for credit loss	$ 88.2	$ 60.3
Percentage of financing receivable, before allowance for credit loss	0.289	0.234
1.0 to 1.5
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated current year	$ 23.9	$ 40.1
Financing receivable, originated year one	39.6	0.0
Financing receivable, originated year two	0.0	0.0
Financing receivable, originated year three	0.0	0.0
Financing receivable, originated year four	0.0	0.0
Prior	7.1	9.9
Financing receivable, before allowance for credit loss	$ 70.6	$ 50.0
Percentage of financing receivable, before allowance for credit loss	0.231	0.194
Less than 1.0
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated current year	$ 0.0	$ 0.0
Financing receivable, originated year one	0.0	0.0
Financing receivable, originated year two	0.0	0.0
Financing receivable, originated year three	0.0	0.0
Financing receivable, originated year four	0.0	5.8
Prior	5.3	6.1
Financing receivable, before allowance for credit loss	$ 5.3	$ 11.9
Percentage of financing receivable, before allowance for credit loss	0.017	0.046
Total
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated current year	$ 74.8	$ 133.5
Financing receivable, originated year one	134.6	5.6
Financing receivable, originated year two	2.7	0.0
Financing receivable, originated year three	0.0	4.7
Financing receivable, originated year four	4.6	9.8
Prior	88.8	104.0
Financing receivable, before allowance for credit loss	$ 305.5	$ 257.6
Percentage of financing receivable, before allowance for credit loss	1.000	1.000
70% and less
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated current year	$ 43.9	$ 71.7
Financing receivable, originated year one	68.8	5.6
Financing receivable, originated year two	0.0	0.0
Financing receivable, originated year three	0.0	0.0
Financing receivable, originated year four	0.0	4.0
Prior	85.9	99.8
Financing receivable, before allowance for credit loss	$ 198.6	$ 181.1
Percentage of financing receivable, before allowance for credit loss	0.650	0.703
71% to 80%
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated current year	$ 30.9	$ 61.8
Financing receivable, originated year one	44.8	0.0
Financing receivable, originated year two	2.7	0.0
Financing receivable, originated year three	0.0	4.7
Financing receivable, originated year four	4.6	0.0
Prior	1.0	1.0
Financing receivable, before allowance for credit loss	$ 84.0	$ 67.5
Percentage of financing receivable, before allowance for credit loss	0.275	0.262
81% to 95%
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated current year	$ 0.0	$ 0.0
Financing receivable, originated year one	21.0	0.0
Financing receivable, originated year two	0.0	0.0
Financing receivable, originated year three	0.0	0.0
Financing receivable, originated year four	0.0	0.0
Prior	0.0	1.1
Financing receivable, before allowance for credit loss	$ 21.0	$ 1.1
Percentage of financing receivable, before allowance for credit loss	0.069	0.004
Greater than 95%
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated current year	$ 0.0	$ 0.0
Financing receivable, originated year one	0.0	0.0
Financing receivable, originated year two	0.0	0.0
Financing receivable, originated year three	0.0	0.0
Financing receivable, originated year four	0.0	5.8
Prior	1.9	2.1
Financing receivable, before allowance for credit loss	$ 1.9	$ 7.9
Percentage of financing receivable, before allowance for credit loss	0.006	0.031
Total
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated current year	$ 74.8	$ 133.5
Financing receivable, originated year one	134.6	5.6
Financing receivable, originated year two	2.7	0.0
Financing receivable, originated year three	0.0	4.7
Financing receivable, originated year four	4.6	9.8
Prior	88.8	104.0
Financing receivable, before allowance for credit loss	$ 305.5	$ 257.6
Percentage of financing receivable, before allowance for credit loss	1.000	1.000

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Amortized cost of financing receivable originated more than five years prior to current fiscal year. Excludes net investment in lease.

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