The components of net investment income were as follows:


YEARS ENDED DECEMBER 31	2022			2021			2020
(in millions)
Fixed maturities	$	239.3		$	216.9		$	222.5
Limited partnerships		35.7			68.2			16.7
Mortgage loans		16.1			18.0			17.5
Equity securities		12.0			15.6			14.8
Other investments		4.6			3.0			3.2
Gross investment income		307.7			321.7			274.7
Less: investment expenses		(11.4	)		(11.0	)		(9.6	)
Net investment income	$	296.3		$	310.7		$	265.1

The change in fair value of limited partnerships measured using NAV is reported in net investment income, of which $2.0 million of holding losses were related to securities still owned at December 31, 2022, $17.1 million of holding gains and $6.9 million of holding losses were related to securities still owned at December 31, 2021 and 2020, respectively.

There were no fixed maturity securities on non-accrual status at December 31, 2022 or 2021, and there was no effect on income for the year ended December 31, 2022. The effects of non-accruals for the years ended December 31, 2021 and 2020, compared with amounts of net investment income that would have been recognized in accordance with the original terms of the fixed maturities were not material.

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


YEARS ENDED DECEMBER 31	2022			2021		2020
(in millions)
Equity securities	$	(63.3	)	$	119.1	$	13.4
Fixed maturities		(45.2	)		1.7		(4.2	)
Other investments		(0.3	)		1.5		2.5
Mortgage loans		2.3			0.7		(6.7	)
Net realized and unrealized investment gains	$	(106.5	)	$	123.0	$	5.0

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


YEARS ENDED DECEMBER 31	2022			2021		2020
(in millions)
Net gains (losses) recognized during the period	$	(63.3	)	$	119.1	$	13.4
Less: net gains (losses) recognized on equity securities sold during the period		(42.7	)		2.2		(19.8	)
Net unrealized gains (losses) recognized during the period on equity securities still held	$	(20.6	)	$	116.9	$	33.2

Included in net realized and unrealized investment gains (losses) for the years ended December 31, 2022, 2021 and 2020, were net impairments of investment securities totaling $16.7 million, $0.7 million and $26.3 million, respectively. In 2022, impairments consisted of $18.5 million on fixed maturities, partially offset by recoveries of $1.8 million of estimated credit losses on mortgage loans. Impairments on fixed maturities included $14.8 million related to intent to sell securities and $3.7 million of estimated credit losses. 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. In 2020, impairments primarily consisted of $17.6 million on fixed maturities and $6.7 million of estimated credit losses on mortgage loans. Impairments on fixed maturities included $16.5 million relating to intent to sell securities and $1.1 million of estimated credit losses.

At December 31, 2022 and 2021, the allowance for credit losses on mortgage loans was $3.2 million and $7.1 million, respectively, and the allowance for credit losses on available-for-sale securities was $2.1 million and $0.3 million, respectively.

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

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.

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.

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	2022		2021		2020
(in millions)
Proceeds from sales	$	489.0	$	485.0	$	264.1
Gross gains		4.4		6.4		9.9
Gross losses		34.1		16.9		2.9