YEARS ENDED DECEMBER 31	2020			2019			2018
(in millions)
Fixed maturities	$	222.5		$	232.4		$	217.7
Mortgage loans		17.5			16.3			14.0
Limited partnerships		16.7			19.7			24.1
Equity securities		14.8			16.3			17.0
Other investments		3.2			5.3			4.8
Gross investment income		274.7			290.0			277.6
Less: investment expenses		(9.6	)		(8.7	)		(10.2	)
Net investment income	$	265.1		$	281.3		$	267.4

The change in fair value of limited partnerships measured using NAV is reported in net investment income, of which, $6.9 million and $4.6 million of holding losses related to securities still owned at December 21, 2020 and 2019, respectively, and $5.3 million of holding gains related to securities still owned at December 31, 2018.

The carrying values of fixed maturity securities on non-accrual status at December 31, 2020 and 2019 were not material. The effects of non-accruals for the years ended December 31, 2020, 2019 and 2018, compared with amounts of net investment income that would have been recognized in accordance with the original terms of the fixed maturities were also not material.

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

YEARS ENDED DECEMBER 31	2020			2019			2018
(in millions)
Equity securities	$	13.4		$	106.5		$	(43.4	)
Other investments		2.5			—			(1.3	)
Mortgage loans		(6.7	)		(0.2	)		(0.2	)
Fixed maturities		(4.2	)		3.1			(5.8	)
Net realized and unrealized investment gains (losses)	$	5.0		$	109.4		$	(50.7	)

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

YEARS ENDED DECEMBER 31		2020			2019		2018
(in millions)
Net gains (losses) recognized during the period	$	13.4		$	106.5	$	(43.4	)
Less: net (losses) gains recognized on equity securities sold during the period		(19.8	)		2.8		(3.9	)
Net unrealized gains (losses) recognized during the period on equity securities still held	$	33.2		$	103.7	$	(39.5	)

Included in net realized and unrealized investment gains (losses) for the years ended December 31, 2020, 2019 and 2018, were impairments of investment securities totaling $26.3 million, $2.0 million and $4.6 million, respectively. 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 intend-to-sell securities and $1.1 million of estimated credit losses. In 2019, impairments consisted entirely of corporate fixed maturity securities. In 2018, impairments consisted of $2.6 million on fixed maturities and $2.0 million on other invested assets.

See Note 1, “Summary of Significant Accounting Policies — New Accounting Pronouncements: Recently Implemented Standards,” for a discussion of new guidance effective January 1, 2020, which affects the accounting for expected credit losses on fixed maturity securities and mortgage loans. Under the new guidance, credit losses on fixed maturities continue to be measured based on the present value of expected future cash flows compared to amortized cost; however, credit losses on available-for-sale fixed maturities are now recognized through an allowance instead of a direct write down of amortized cost. The new guidance stipulates that recoveries of previously recorded credit losses are recorded immediately as a reversal of the allowance. In addition, the allowance is limited to the amount that fair value is less than amortized cost and therefore, increases in the fair value of investments due to reasons other than credit could result in decreases in the allowance. Changes in the allowance for credit losses are recorded in net realized and unrealized investment gains (losses). At December 31, 2020 and 2019, the allowance for credit losses on mortgage loans was $7.9 million and

$1.3 million, respectively. The allowance for credit losses on available-for-sale securities was $0.1 million at December 31, 2020. There was no allowance for credit losses on available-for-sale securities at December 31, 2019.

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
(in millions)
	Proceeds		Gross		Gross
2020	from Sales		Gains		Losses
Fixed maturities	$	264.1	$	9.9	$	2.9

2019
Fixed maturities, excluding held-for-sale (Chaucer)	$	541.2	$	6.9	$	5.7
Fixed maturities, held-for-sale		0.3		—		—
Total fixed maturities	$	541.5	$	6.9	$	5.7

2018
Fixed maturities, excluding held-for-sale (Chaucer)	$	296.5	$	2.1	$	8.4
Fixed maturities, held-for-sale		276.8		1.7		1.7
Total fixed maturities	$	573.3	$	3.8	$	10.1