The components of net investment income were as follows:


YEARS ENDED DECEMBER 31	2023			2022			2021
(in millions)
Fixed maturities	$	283.2		$	239.3		$	216.9
Limited partnerships		30.0			35.7			68.2
Mortgage loans		15.8			16.1			18.0
Equity securities		6.4			12.0			15.6
Other investments		10.6			4.6			3.0
Gross investment income		346.0			307.7			321.7
Less: investment expenses		(13.9	)		(11.4	)		(11.0	)
Net investment income	$	332.1		$	296.3		$	310.7

The change in fair value of limited partnerships measured using NAV is reported in net investment income, of which $8.1 million and $2.0 million of holding losses were related to securities owned at December 31, 2023 and 2022, respectively, and $17.1 million of holding gains were related to securities owned at December 31, 2021.

The carrying value of fixed maturity securities on non-accrual status at December 31, 2023 was $14.8 million, and there were no fixed maturity securities on non-accrual status at December 31, 2022. The effects on income of non-accruals compared with amounts that would have been recognized in accordance with the original terms of the fixed maturities were not material for the years ended December 31, 2023, 2022 and 2021.

Net realized and unrealized gains (losses) on investments, including impairments, were as follows:


YEARS ENDED DECEMBER 31	2023			2022			2021
(in millions)
Fixed maturities	$	(20.2	)	$	(45.2	)	$	1.7
Mortgage loans		(6.9	)		2.3			0.7
Equity securities		(5.6	)		(63.3	)		119.1
Other investments		0.2			(0.3	)		1.5
Net realized and unrealized investment gains (losses)	$	(32.5	)	$	(106.5	)	$	123.0

The following table provides pre-tax net realized and unrealized gains (losses) on equity securities:


YEARS ENDED DECEMBER 31	2023			2022			2021
(in millions)
Net gains (losses) recognized during the period	$	(5.6	)	$	(63.3	)	$	119.1
Less: net gains (losses) recognized on equity securities sold during the period		(11.6	)		(42.7	)		2.2
Net unrealized gains (losses) recognized during the period on equity securities still held	$	6.0		$	(20.6	)	$	116.9

Included in net realized and unrealized investment gains (losses) for the years ended December 31, 2023, 2022 and 2021, were net impairments of investment securities totaling $18.0 million, $16.7 million and $0.7 million, respectively. In 2023, impairments consisted of $11.1 million on fixed maturities, primarily related to intent to sell securities, and $6.9 million of estimated credit losses on mortgage loans. In 2022, impairments consisted of $18.5 million on fixed maturities, of which $14.8 million related to intent to sell securities and $3.7 million related to estimated credit losses. These impairments were partially offset by recoveries of $1.8 million of estimated credit losses on mortgage loans. In 2021, impairments consisted of $1.3 million on fixed maturities, offset by recoveries of $0.6 million of estimated credit losses on mortgage loans.

At December 31, 2023 and 2022, the allowance for credit losses on mortgage loans was $10.0 million and $3.2 million, respectively, and the allowance for credit losses on available-for-sale securities was $1.9 million and $2.1 million, respectively. The following table provides rollforwards of the allowance for credit losses on mortgage loans:


YEARS ENDED DECEMBER 31	2023			2022
(in millions)
Allowance for credit losses as of the beginning of the period	$	3.2		$	7.1
Additional credit losses on investments for which an allowance was previously recognized		6.9			0.2
Reductions for disposals		(0.1	)		(2.1	)
Recoveries		—			(2.0	)
Allowance for credit losses as of the end of the period	$	10.0		$	3.2

The methodology and significant inputs used to measure the amount of credit losses were as follows:

Mortgage loans – the Company estimated losses by applying expected loss rates, which are based on historical data. Embedded in expected loss rates are mortgage risk ratings and risk factors associated with property type such as office, retail, lodging, multi-family and industrial. Risk ratings, based on property characteristics and metrics including the geographic market, are predominantly driven by estimates of loan-to-value and debt service coverage ratios. Ratings may be adjusted to reflect current conditions and to incorporate reasonable and supportable forecasts, such as volatility of cash flows and valuation.

Fixed maturities, Corporate bonds – the Company utilized a financial model that derives expected cash flows based on probability-of-default factors by credit rating and asset duration, and loss-given-default factors based on security type. These factors are based on historical data provided by an independent third-party rating agency. In addition, other qualitative market data relevant to the realizability of contractual cash flows may be considered, including current conditions and reasonable and supportable forecasts.

The proceeds from sales of available-for-sale fixed maturities, and the gross realized gains and gross realized losses on those sales, were as follows:



YEARS ENDED DECEMBER 31	2023		2022		2021
(in millions)
Proceeds from sales	$	168.8	$	489.0	$	485.0
Gross gains		1.0		4.4		6.4
Gross losses		10.5		34.1		16.9