Investments, Debt and Equity Securities [Abstract]

Investments Classified by Contractual Maturity Date

The amortized cost and fair value by maturity periods for fixed maturities are shown in the following table. Actual maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties, or the Company may have the right to put or sell the obligations back to the issuers.


DECEMBER 31	2023
(in millions)	Amortized Cost, net of Allowance for Credit Losses		Fair Value
Due in one year or less	$	473.1	$	468.6
Due after one year through five years		2,670.4		2,582.8
Due after five years through ten years		2,433.1		2,177.3
Due after ten years		299.7		271.0
		5,876.3		5,499.7
Mortgage-backed and other asset-backed securities		2,697.6		2,485.6
Total fixed maturities	$	8,573.9	$	7,985.3

Schedule of Unrealized Loss on Investments

The following tables provide information about the Company’s available-for-sale fixed maturity securities that were in an unrealized loss position at December 31, 2023 and 2022, including the length of time the securities have been in an unrealized loss position:


DECEMBER 31, 2023	12 months or less				Greater than 12 months				Total
(in millions)	Gross				Gross				Gross
	Unrealized		Fair		Unrealized		Fair		Unrealized		Fair
	Losses		Value		Losses		Value		Losses		Value
Investment grade:
U.S. Treasury and government agencies	$	0.6	$	62.2	$	51.1	$	331.0	$	51.7	$	393.2
Foreign governments		—		—		—		2.0		—		2.0
Municipal		2.5		72.5		127.1		935.2		129.6		1,007.7
Corporate		1.3		159.9		214.9		2,870.2		216.2		3,030.1
Residential mortgage-backed		1.2		139.3		129.0		865.4		130.2		1,004.7
Commercial mortgage-backed		0.2		14.0		72.0		770.0		72.2		784.0
Other asset-backed		0.1		28.1		15.8		260.2		15.9		288.3
Total investment grade		5.9		476.0		609.9		6,034.0		615.8		6,510.0
Below investment grade:
Corporate		2.5		33.8		6.4		66.2		8.9		100.0
Commercial mortgage-backed		—		—		—		0.9		—		0.9
Total below investment grade		2.5		33.8		6.4		67.1		8.9		100.9
Total fixed maturities	$	8.4	$	509.8	$	616.3	$	6,101.1	$	624.7	$	6,610.9


DECEMBER 31, 2022	12 months or less				Greater than 12 months				Total
(in millions)	Gross				Gross				Gross
	Unrealized		Fair		Unrealized		Fair		Unrealized		Fair
	Losses		Value		Losses		Value		Losses		Value
Investment grade:
U.S. Treasury and government agencies	$	15.8	$	237.3	$	43.1	$	160.7	$	58.9	$	398.0
Foreign governments		0.1		1.9		—		—		0.1		1.9
Municipal		64.9		595.5		99.3		386.6		164.2		982.1
Corporate		202.2		2,786.2		118.2		489.8		320.4		3,276.0
Residential mortgage-backed		51.6		642.0		90.5		387.6		142.1		1,029.6
Commercial mortgage-backed		48.7		663.2		39.0		164.4		87.7		827.6
Other asset-backed		11.0		234.8		16.0		75.1		27.0		309.9
Total investment grade		394.3		5,160.9		406.1		1,664.2		800.4		6,825.1
Below investment grade:
Corporate		13.5		253.2		3.8		17.3		17.3		270.5
Total fixed maturities	$	407.8	$	5,414.1	$	409.9	$	1,681.5	$	817.7	$	7,095.6

Schedule of Amortized Cost of Mortgage Participations and Other Loans by Credit Ratings and Year of Origination

The amortized cost of mortgage participations and other loans by credit ratings and year of origination was as follows:


DECEMBER 31, 2023
(in millions)	Prior to 2019		2019		2020		2021		2022		2023		Total
Credit Quality
Aaa/Aa/A	$	140.2	$	34.8	$	9.7	$	62.2	$	10.0	$	—	$	256.9
Baa		41.3		12.4		17.5		—		—		—		71.2
Ba and lower		47.4		—		5.9		—		—		—		53.3
Amortized cost	$	228.9	$	47.2	$	33.1	$	62.2	$	10.0	$	—	$	381.4
Allowance for credit losses														(10.0	)
Amortized cost, net of allowance for credit losses													$	371.4