Investments

The following table provides cost or amortized cost, gross unrealized gains, gross unrealized losses and fair value for our fixed-maturity securities:



(Dollars in millions)	Cost or amortized cost		Gross unrealized				Fair value
At March 31, 2019	Cost or amortized cost		gains		losses		Fair value
Fixed maturity securities:
Corporate	$	5,753	$	160	$	25	$	5,888
States, municipalities and political subdivisions	4,269		153		3		4,419
Government-sponsored enterprises	305		—		3		302
Commercial mortgage-backed	292		6		1		297
United States government	99		1		—		100
Foreign government	16		—		—		16
Total	$	10,734	$	320	$	32	$	11,022
At December 31, 2018
Fixed maturity securities:
Corporate	$	5,712	$	85	$	87	$	5,710
States, municipalities and political subdivisions	4,251		84		31		4,304
Government-sponsored enterprises	316		1		7		310
Commercial mortgage-backed	287		3		2		288
United States government	67		1		1		67
Foreign government	10		—		—		10
Total	$	10,643	$	174	$	128	$	10,689

The net unrealized investment gains in our fixed-maturity portfolio at March 31, 2019, are primarily the result of the continued low interest rate environment that increased the fair value of our fixed-maturity portfolio. Our commercial mortgage-backed securities had an average rating of Aa1/AA at March 31, 2019, and December 31, 2018. At March 31, 2019, Microsoft Corporation (Nasdaq:MSFT) was our largest single equity holding with a fair value of

$296 million, which was 4.6% of our publicly traded common equities portfolio and 1.7% of the total investment portfolio.

The table below provides fair values and gross unrealized losses by investment category and by the duration of the securities’ continuous unrealized loss positions:



(Dollars in millions)	Less than 12 months				12 months or more				Total
At March 31, 2019	Fair value		Unrealized losses		Fair value		Unrealized losses		Fair value		Unrealized losses
Fixed maturity securities:
Corporate	$	343	$	5	$	685	$	20	$	1,028	$	25
States, municipalities and political subdivisions	10		—		237		3		247		3
Government-sponsored enterprises	7		—		204		3		211		3
Commercial mortgage-backed securities	2		—		45		1		47		1
United States government	—		—		23		—		23		—
Total	$	362	$	5	$	1,194	$	27	$	1,556	$	32
At December 31, 2018
Fixed maturity securities:
Corporate	$	2,082	$	51	$	501	$	36	$	2,583	$	87
States, municipalities and political subdivisions	823		18		340		13		1,163		31
Government-sponsored enterprises	49		1		211		6		260		7
Commercial mortgage-backed	77		—		64		2		141		2
United States government	—		—		33		1		33		1
Total	$	3,031	$	70	$	1,149	$	58	$	4,180	$	128

Contractual maturity dates for fixed-maturities investments were:



(Dollars in millions)	Amortized cost		Fair value		% of fair value
At March 31, 2019	Amortized cost		Fair value		% of fair value
Maturity dates:
Due in one year or less	$	598	$	604	5.5	%
Due after one year through five years	2,977		3,039		27.6
Due after five years through ten years	3,656		3,742		33.9
Due after ten years	3,503		3,637		33.0
Total	$	10,734	$	11,022	100.0	%

Actual maturities may differ from contractual maturities when there is a right to call or prepay obligations with or without call or prepayment penalties.

The following table provides investment income and investment gains and losses, net:



(Dollars in millions)	Three months ended March 31,
	2019		2018
Investment income:
Interest	$	111	$	110
Dividends	46		42
Other	3		1
Total	160		153
Less investment expenses	3		3
Total	$	157	$	150

Investment gains and losses, net:
Equity securities:
Investment gains and losses on securities sold, net	$	4	$	3
Unrealized gains and losses on securities still held, net	652		(198		)
Subtotal	656		(195		)
Fixed maturities:
Gross realized gains	2		4
Subtotal	2		4

Other	5		—
Total	$	663	$	(191	)

During the three months ended March 31, 2019 and 2018, there were no fixed-maturity securities other-than-temporarily impaired. There were no credit losses on fixed-maturity securities for which a portion of other-than-temporary impairment (OTTI) has been recognized in other comprehensive income for the three months ended March 31, 2019 and 2018.

At March 31, 2019, 358 fixed-maturity securities with a total unrealized loss of $27 million had been in an unrealized loss position for 12 months or more. Of that total, no fixed-maturity security had a fair value below 70% of amortized cost. At December 31, 2018, 400 fixed-maturity securities with a total unrealized loss of $58 million had been in an unrealized loss position for 12 months or more. Of that total, no fixed-maturity securities had fair values below 70% of amortized cost.