At March 31, 2024, the Group’s investments are substantially all managed by external investment managers through individual investment management agreements. The Group monitors activity and performance of the external managers on an ongoing basis.


	March 31, 2024
	Amortized Cost		Unrealized gains		Unrealized losses		Fair value
U.S. Treasuries	$	688.5	$	1.1	$	(5.7)	$	683.9
Agencies	16.3		—		(0.2)		16.1
Non-U.S. government	67.8		—		(1.7)		66.1
Corporate bonds	1,778.2		7.0		(19.7)		1,765.5
Residential mortgage-backed	240.1		1.4		(6.6)		234.9
Commercial mortgage-backed	51.3		—		(1.5)		49.8
Other asset backed securities	412.3		1.5		(3.0)		410.8
Total fixed maturity securities	$	3,254.5	$	11.0	$	(38.4)	$	3,227.1


	December 31, 2023
	Amortized Cost		Unrealized gains		Unrealized losses		Fair value
U.S. Treasuries	$	692.4	$	4.1	$	(9.8)	$	686.7
Agencies	16.2		0.1		(0.1)		16.2
Non-U.S. government	77.6		0.2		(1.8)		76.0
Corporate bonds	1,798.4		14.7		(25.8)		1,787.3
Residential mortgage-backed	192.0		2.0		(5.8)		188.2
Commercial mortgage-backed	53.1		—		(2.0)		51.1
Other asset backed securities	441.7		1.3		(3.6)		439.4
Total fixed maturity securities	$	3,271.4	$	22.4	$	(48.9)	$	3,244.9

Review of the fixed maturity securities is performed on a regular basis to consider concentration, credit quality and compliance with established guidelines. For individual fixed maturity securities, nationally recognized statistical rating organizations (“NRSROs”) are used and the lower of two or middle of three ratings is taken. The composition of the fair values of fixed maturity securities by credit rating is as follows:


	March 31, 2024				December 31, 2023
	Fair Value		%		Fair Value		%
AAA	$	383.0	12	%	$	399.5	12	%
AA	1,182.6		36	%	1,119.0		35	%
A	1,285.5		40	%	1,145.8		35	%
BBB	373.0		12	%	573.6		18	%
BB	3.0		—	%	7.0		—	%
Total fixed maturity securities	$	3,227.1	100	%	$	3,244.9	100	%


	March 31, 2024				December 31, 2023
	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Due in one year or less	$	464.3	$	457.1	$	566.7	$	555.9
Due after one year through five years	2,110.4		2,097.4		2,130.3		2,119.5
Due after five years through ten years	319.9		318.2		255.5		256.0
Due after ten years	359.9		354.4		318.9		313.5
Total fixed maturity securities	$	3,254.5	$	3,227.1	$	3,271.4	$	3,244.9

Expected maturities may differ from contractual maturities as borrowers may have the right to call or repay obligations with or without call or prepayment penalties. Additionally, lenders may have the right to put the securities back to the borrower.


	March 31, 2024
	Amortized Cost		Unrealized gains		Unrealized losses		Fair value
U.S. Treasuries	$	76.3	$	—	$	—	$	76.3


Total short-term investments	$	76.3	$	—	$	—	$	76.3


	December 31, 2023
	Amortized Cost		Unrealized gains		Unrealized losses		Fair value
U.S. Treasuries	$	49.0	$	—	$	—	$	49.0


Total short-term investments	$	49.0	$	—	$	—	$	49.0


	March 31, 2024				December 31, 2023
	Fair Value		%		Fair Value		%

AA	76.3		100	%	49.0		100	%


Total short-term investments	$	76.3	100	%	$	49.0	100	%

The following table summarizes, by type of security, the aggregate fair value and gross unrealized loss by length of time the security has been in an unrealized loss position for the Group’s available-for-sale portfolio:


	March 31, 2024
			0 - 12 months		> 12 months
	Fair value		Gross unrealized losses		Gross unrealized losses		Number of securities
U.S. Treasuries	$	459.8	$	(2.4)	$	(3.3)	54
Agencies	10.0		—		(0.2)		8
Non-U.S. government	58.6		(0.2)		(1.5)		31
Corporate bonds	958.2		(2.8)		(16.9)		507
Residential mortgage-backed	112.3		(0.7)		(5.9)		67
Commercial mortgage-backed	36.9		—		(1.5)		21
Other asset backed securities	163.8		(0.6)		(2.4)		57
Total	$	1,799.6	$	(6.7)	$	(31.7)	745


	December 31, 2023
			0 - 12 months		> 12 months
	Fair value		Gross unrealized losses		Gross unrealized losses		Number of securities
U.S. Treasuries	$	362.2	$	(0.2)	$	(9.6)	52
Agencies	5.9		—		(0.1)		5
Non-U.S. government	51.3		—		(1.8)		29
Corporate bonds	894.8		(0.9)		(24.9)		527
Residential mortgage-backed	84.3		(0.2)		(5.6)		54
Commercial mortgage-backed	43.2		(0.1)		(1.9)		23
Other asset backed securities	208.2		(0.3)		(3.3)		74
Total	$	1,649.9	$	(1.7)	$	(47.2)	764

At March 31, 2024 on a security level basis, 745 securities out of a total of approximately 1,196 securities were in an unrealized loss position and the largest single unrealized loss from a single security in the Group’s fixed maturity portfolio was $0.7 million. The Group believes that such securities were temporarily impaired at March 31, 2024. At December 31, 2023, on a security level basis, approximately 764 securities out of a total of approximately 1,263 securities were in an unrealized loss position and the largest single unrealized loss from a single security in the Group’s fixed maturity portfolio was $1.7 million.

The following table provides a roll forward of the allowance for expected credit losses of the Group’s securities classified as available-for-sale:


	Three months ended
	March 31, 2024		March 31, 2023
Balance at beginning of period	$	1.3	$	1.1
Expected credit losses on securities where credit losses were not previously recognized	0.5		0.8
Additions for expected credit losses on securities where credit losses were previously recognized	0.8		0.6

Securities sold/redeemed/matured	(0.2)		—
Balance at end of period	$	2.4	$	2.5

The Group assesses each quarter whether the decline in the fair value of an available-for-sale investment below its amortized cost is the result of a credit loss. All available-for-sale securities with unrealized losses are reviewed. The Group considers many factors to

determine whether a credit loss exists, including the extent to which fair value is below cost, the implied yield to maturity, rating downgrades of the security and whether or not the issuer has failed to make scheduled principal or interest payments. The Group also takes into consideration information about the financial condition of the issuer and industry factors that could negatively impact the capital markets.

If the decline in fair value of an available-for-sale security below its amortized cost is considered to be the result of a credit loss, the Group compares the estimated present value of the cash flows expected to be collected to the amortized cost of the security. The extent to which the estimated present value of the cash flows expected to be collected is less than the amortized cost of the security represents the expected credit loss, which is recorded as an allowance and recognized in net income.

At March 31, 2024, other investments consisted primarily of an opportunistic fixed income UCITS fund managed by Wellington Investment Management ("Wellington Funds").


	March 31, 2024				December 31, 2023
	Fair Value		%		Fair Value		%
Wellington Funds	$	46.4	99	%	$	46.9	99	%
Other securities valued at net asset value per share	0.6		1	%	0.6		1	%


Total other investments at fair value	$	47.0	100	%	$	47.5	100	%

In 2021 the Group invested $50.0 million in Wellington Funds. The fair value of the investment at March 31, 2024 was $46.4 million (December 31, 2023 - $46.9 million).


	Three Months Ended
	March 31, 2024		March 31, 2023
Net interest and dividend income	$	42.1	$	21.3
Investment expenses	(1.1)		(0.9)
Net investment income	41.0		20.4
Net realized losses on fixed maturity securities, available-for-sale	(7.4)		—

Net realized gains on other investments	—		2.2


Change in net unrealized (losses)/gains on other investments	(0.5)		2.0

Provision for expected credit losses	(1.1)		(1.4)
Net realized and unrealized investment (losses)/gains	(9.0)		2.8
Total realized and unrealized investments gains/(losses) and net investment income	$	32.0	$	23.2