The amortized cost and fair value of available-for-sale fixed maturities were as follows:

DECEMBER 31, 2020
(in millions)

	Amortized Cost		Allowance for Credit Losses			Amortized Cost, Net of Allowance for Credit Losses		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
U.S. Treasury and government agencies	$	376.4	$	—		$	376.4	$	17.6	$	2.0	$	392.0
Foreign government		2.2		—			2.2		0.5		—		2.7
Municipal		1,042.1		—			1,042.1		61.7		0.1		1,103.7
Corporate		3,770.0		(0.1	)		3,769.9		341.8		0.4		4,111.3
Residential mortgage-backed		978.2		—			978.2		33.1		0.6		1,010.7
Commercial mortgage-backed		705.4		—			705.4		54.8		0.2		760.0
Asset-backed		71.4		—			71.4		2.6		—		74.0
Total fixed maturities	$	6,945.7	$	(0.1	)	$	6,945.6	$	512.1	$	3.3	$	7,454.4

DECEMBER 31, 2019
(in millions)			Gross		Gross				OTTI
	Amortized		Unrealized		Unrealized				Unrealized
	Cost		Gains		Losses		Fair Value		Losses⁽¹⁾
U.S. Treasury and government agencies	$	342.0	$	9.1	$	1.3	$	349.8	$	—
Foreign government		15.7		0.4		—		16.1		—
Municipal		807.1		27.6		1.2		833.5		—
Corporate		3,653.5		161.6		3.9		3,811.2		3.0
Residential mortgage-backed		905.4		17.1		1.1		921.4		—
Commercial mortgage-backed		666.4		25.6		0.1		691.9		—
Asset-backed		62.1		1.1		—		63.2		—
Total fixed maturities	$	6,452.2	$	242.5	$	7.6	$	6,687.1	$	3.0

The Company enters into various agreements that may require its fixed maturities to be held as collateral by others. At December 31, 2020 and 2019, fixed maturities with fair values of $103.9 million and $94.0 million, respectively, were held as collateral for the FHLB collateralized borrowing program. See Note 6 — “Debt and Credit Arrangements” for additional information related to the Company’s FHLB program. Additionally, at December 31, 2020 and 2019, fixed maturities with fair values of $315.2 million and $308.7 million, respectively, were on deposit with various state governmental authorities or trustees.

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	2020
(in millions)	Amortized Cost, net of Allowance for Credit Losses		Fair Value
Due in one year or less	$	334.1	$	339.1
Due after one year through five years		1,774.6		1,913.3
Due after five years through ten years		2,306.3		2,548.2
Due after ten years		775.6		809.1
		5,190.6		5,609.7
Mortgage-backed and asset-backed securities		1,755.0		1,844.7
Total fixed maturities	$	6,945.6	$	7,454.4

Unrealized gains and losses on available-for-sale and other securities are summarized in the following table.

YEARS ENDED DECEMBER 31
(in millions)				Equity
	Fixed			Securities and
2020	Maturities			Other			Total
Net appreciation, beginning of year	$	216.0		$	—		$	216.0
Net appreciation on available-for-sale securities		280.2			—			280.2
Provision for deferred income taxes		(68.1	)		—			(68.1	)
		212.1			—			212.1
Net appreciation, end of year	$	428.1		$	—		$	428.1

2019
Net depreciation, beginning of year	$	(27.2	)	$	—		$	(27.2	)
Net appreciation on available-for-sale securities		324.7			—			324.7
Provision for deferred income taxes		(83.0	)		—			(83.0	)
Cumulative effect adjustment for ASU 2017-08, net of tax		1.5			—			1.5
		243.2			—			243.2
Net appreciation, end of year	$	216.0		$	—		$	216.0

2018
Net appreciation, beginning of year	$	110.1		$	95.3		$	205.4
Net depreciation on available-for-sale securities		(203.7	)		—			(203.7	)
Provision for deferred income taxes		33.6			—			33.6
Amount realized with sale of Chaucer, net of tax		19.1			—			19.1
Cumulative effect adjustment for ASUs 2016-01 and 2018-02, net of tax		13.7			(95.3	)		(81.6	)
		(137.3	)		(95.3	)		(232.6	)
Net depreciation, end of year	$	(27.2	)	$	—		$	(27.2	)

Effective January 1, 2018, increases or decreases in fair value of equity securities are no longer reported as unrealized gains and losses in accumulated other comprehensive income. Instead, they are reported in net realized and unrealized investment gains (losses) in the Consolidated Statements of Income.

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, 2020 and 2019 including the length of time the securities have been in an unrealized loss position:

DECEMBER 31, 2020	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	$	2.0	$	140.7	$	—	$	—	$	2.0	$	140.7
Municipal		0.1		19.3		—		0.7		0.1		20.0
Corporate		0.4		53.4		—		—		0.4		53.4
Residential mortgage-backed		0.6		94.4		—		—		0.6		94.4
Commercial mortgage-backed		0.2		33.2		—		—		0.2		33.2
Total investment grade		3.3		341.0		—		0.7		3.3		341.7
Below investment grade:
Corporate		—		4.6		—		—		—		4.6
Total fixed maturities	$	3.3	$	345.6	$	—	$	0.7	$	3.3	$	346.3

DECEMBER 31, 2019	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	$	1.3	$	73.0	$	—	$	9.3	$	1.3	$	82.3
Municipal		1.1		72.5		0.1		5.6		1.2		78.1
Corporate		0.7		86.5		0.1		4.7		0.8		91.2
Residential mortgage-backed		0.7		69.2		0.4		34.4		1.1		103.6
Commercial mortgage-backed		0.1		40.6		—		0.9		0.1		41.5
Asset-backed		—		—		—		1.7		—		1.7
Total investment grade		3.9		341.8		0.6		56.6		4.5		398.4
Below investment grade:
Corporate		2.2		27.1		0.9		9.0		3.1		36.1
Total fixed maturities	$	6.1	$	368.9	$	1.5	$	65.6	$	7.6	$	434.5

The Company views gross unrealized losses on fixed maturities as non-credit related and through its assessment of unrealized losses has determined that these securities will recover, allowing the Company to realize the anticipated long-term economic value. The Company currently does not intend to sell, nor does it expect to be required to sell these securities before recovery of their amortized cost. The Company employs a systematic methodology to evaluate declines in fair value below amortized cost for fixed maturity securities. In determining impairments, the Company evaluates several factors and circumstances, including the issuer’s overall financial condition; the issuer’s credit and financial strength ratings; the issuer’s financial performance, including earnings trends and asset quality; any specific events which may influence the operations of the issuer; the general outlook for market conditions in the industry or geographic region in which the issuer operates; and the degree to which the fair value of an issuer’s securities is below the Company’s amortized cost. The Company also considers any factors that might raise doubt about the issuer’s ability to make contractual payments as they come due and whether the Company expects to recover the entire amortized cost basis of the security.

The Company’s mortgage participations and other mortgage loans were $467.6 million and $441.2 million at December 31, 2020 and 2019, respectively. Participating interests in commercial mortgage loans are originated and serviced by a third-party. For these investments, the Company shares, on a pro-rata basis, in all related cash flows of the underlying mortgages. Mortgage participations and other mortgage loans were comprised of the following property types and geographic locations.

DECEMBER 31	2020			2019
(in millions)
Property Type:
Office	$	160.4		$	138.2
Apartments		128.3			125.1
Retail		68.5			66.5
Hotel		62.7			62.1
Industrial		55.6			50.6
Valuation allowance		(7.9	)		(1.3	)
Total	$	467.6		$	441.2

DECEMBER 31	2020			2019
(in millions)
Geographic Region:
Pacific	$	117.0		$	102.3
South Atlantic		108.3			95.9
Mid-Atlantic		73.8			53.3
West South Central		70.8			71.2
New England		43.5			42.5
East North Central		27.8			27.8
Mountain		12.5			12.5
Other		21.8			37.0
Valuation allowance		(7.9	)		(1.3	)
Total	$	467.6		$	441.2

At December 31, 2020, scheduled maturities of mortgage participations and other loans were as follows: due in 2021 - $57.5 million; in 2022 - $27.7 million; 2023 - $16.5 million; 2024 - $77.1 million and thereafter - $288.8 million. Actual maturities could differ from contractual maturities because borrowers may have the right to prepay obligations with or without prepayment penalties and loans may be refinanced. During 2020, the Company did not refinance any loans based on terms that differed from current market rates.

Other investments also include interests in limited partnerships of $312.5 million and $278.5 million at December 31, 2020 and December 31, 2019, respectively.

At December 31, 2020 and 2019, the Company’s exposure to concentration of investments in a single investee that exceeded 10% of shareholders’ equity included securities of U.S. government-sponsored agencies, as well as mortgage participations with a highly rated single third-party of $459.3 million and $432.3 million, respectively.

At December 31, 2020, there were contractual investment commitments of up to $205.3 million.