Investments

The following table provides cost or amortized cost, gross unrealized gains, gross unrealized losses and fair value for our investment portfolio:



(Dollars in millions)	Cost or amortized cost
			Gross unrealized				Fair value
At September 30, 2016			gains		losses		Fair value
Fixed maturity securities:
Corporate	$	5,621	$	375	$	14	$	5,982
States, municipalities and political subdivisions	3,619		222		1		3,840
Commercial mortgage-backed	290		18		—		308
Government-sponsored enterprises	108		—		—		108
Foreign government	10		—		—		10
Convertibles and bonds with warrants attached	5		—		—		5
United States government	4		—		—		4
Subtotal	9,657		615		15		10,257
Equity securities:
Common equities	2,982		2,156		61		5,077
Nonredeemable preferred equities	187		40		—		227
Subtotal	3,169		2,196		61		5,304
Total	$	12,826	$	2,811	$	76	$	15,561
At December 31, 2015
Fixed maturity securities:
Corporate	$	5,294	$	255	$	96	$	5,453
States, municipalities and political subdivisions	3,440		172		1		3,611
Commercial mortgage-backed	287		4		2		289
Government-sponsored enterprises	284		—		6		278
Foreign government	10		—		—		10
Convertibles and bonds with warrants attached	5		—		—		5
United States government	4		—		—		4
Subtotal	9,324		431		105		9,650
Equity securities:
Common equities	2,749		1,787		51		4,485
Nonredeemable preferred equities	189		32		—		221
Subtotal	2,938		1,819		51		4,706
Total	$	12,262	$	2,250	$	156	$	14,356

The net unrealized investment gains in our fixed-maturity portfolio 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 September 30, 2016, and December 31, 2015. The seven largest unrealized investment gains in our common stock portfolio are from Honeywell International Incorporated (NYSE:HON), Exxon Mobil Corporation (NYSE:XOM), The Procter & Gamble Company (NYSE:PG), Johnson & Johnson (NYSE:JNJ), BlackRock Inc. (NYSE:BLK), 3M Co (NYSE:MMM) and Microsoft Corporation (Nasdaq:MSFT), which had a combined gross unrealized gain of $649 million. At September 30, 2016, Apple Inc. (Nasdaq:AAPL) was our largest single common stock holding with a fair value of $158 million, which was 3.1 percent of our publicly traded common stock portfolio and 1.0 percent 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
	Fair value		Unrealized losses		Fair value		Unrealized losses		Fair value		Unrealized losses
At September 30, 2016	Fair value		Unrealized losses		Fair value		Unrealized losses		Fair value		Unrealized losses
Fixed maturity securities:
Corporate	$	166	$	4	$	200	$	10	$	366	$	14
States, municipalities and political subdivisions	128		1		—		—		128		1
Commercial mortgage-backed	8		—		3		—		11		—
Government-sponsored enterprises	43		—		—		—		43		—
Subtotal	345		5		203		10		548		15
Equity securities:
Common equities	177		6		203		55		380		61
Total	$	522	$	11	$	406	$	65	$	928	$	76
At December 31, 2015
Fixed maturity securities:
Corporate	$	1,099	$	63	$	133	$	33	$	1,232	$	96
States, municipalities and political subdivisions	47		1		22		—		69		1
Commercial mortgage-backed	103		2		2		—		105		2
Government-sponsored enterprises	100		2		127		4		227		6
Subtotal	1,349		68		284		37		1,633		105
Equity securities:
Common equities	270		51		—		—		270		51
Nonredeemable preferred equities	35		—		—		—		35		—
Subtotal	305		51		—		—		305		51
Total	$	1,654	$	119	$	284	$	37	$	1,938	$	156

Contractual maturity dates for fixed-maturity investments were:



(Dollars in millions)	Amortized cost		Fair value		% of fair value
At September 30, 2016	Amortized cost		Fair value		% of fair value
Maturity dates:
Due in one year or less	$	446	$	452	4.4	%
Due after one year through five years	3,049		3,265		31.8
Due after five years through ten years	3,856		4,067		39.7
Due after ten years	2,306		2,473		24.1
Total	$	9,657	$	10,257	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, realized investment gains and losses, the change in unrealized investment gains and losses, and other items:



(Dollars in millions)	Three months ended September 30,						Nine months ended September 30,
	2016			2015			2016			2015
Investment income:
Interest	$	111		$	108		$	330		$	319
Dividends	39			37			117			108
Other	1			1			2			2
Total	151			146			449			429
Less investment expenses	3			3			7			7
Total	$	148		$	143		$	442		$	422

Realized investment gains and losses summary:
Fixed maturities:
Gross realized gains	$	10		$	4		$	17		$	14
Gross realized losses	—			—			(1		)	—
Other-than-temporary impairments	—			(8		)	(2		)	(11		)
Equity securities:
Gross realized gains	47			6			147			106
Gross realized losses	—			—			(1		)	(1		)
Other-than-temporary impairments	—			—			—			(1		)
Other	(1		)	1			1			3
Total	$	56		$	3		$	161		$	110

Change in unrealized investment gains and losses:
Fixed maturities	$	(20	)	$	(15	)	$	274		$	(153	)
Equity securities	82			(350		)	367			(574		)
Income tax (provision) benefit	(21		)	127			(224		)	254
Total	$	41		$	(238	)	$	417		$	(473	)

During the three months ended September 30, 2016, there were no equity securities and no fixed-maturity securities other-than-temporarily impaired. During the nine months ended September 30, 2016, there were no equity securities and four 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 and nine months ended September 30, 2016 and 2015. At September 30, 2016, 36 fixed-maturity investments with a total unrealized loss of $10 million had been in an unrealized loss position for 12 months or more. Of that total, one fixed-maturity investment had a fair value below 70 percent of amortized cost. At September 30, 2016, three equity investments with a total unrealized loss of $55 million had been in an unrealized loss position for 12 months or more. Of that total, one equity investment with a total unrealized loss of $36 million had a fair value below 70 percent of amortized cost.

During 2015, we other-than-temporarily impaired 20 securities. At December 31, 2015, 69 fixed-maturity investments with a total unrealized loss of $37 million had been in an unrealized loss position for 12 months or more. Of that total, five fixed-maturity investments had fair values below 70 percent of amortized cost. There were no equity security investments in an unrealized loss position for 12 months or more as of December 31, 2015.