Investments (Tables)

9 Months Ended

Sep. 30, 2016

Investments, Debt and Equity Securities [Abstract]

Investments

The following tables summarize our investments as of the dates indicated:

	September 30, 2016
	Amortized		Gross Unrealized				Estimated Fair
	Cost		Gains		Losses		Value
	(In millions)
Corporate debt securities	$	1,123	$	4	$	—	$	1,127
GSEs	259		—		—		259
Municipal securities	147		1		—		148
Asset-backed securities	76		—		—		76
U.S. treasury notes	65		—		—		65
Certificates of deposit	60		—		—		60
	$	1,730	$	5	$	—	$	1,735

	December 31, 2015
	Amortized		Gross Unrealized				Estimated Fair
	Cost		Gains		Losses		Value
	(In millions)
Corporate debt securities	$	1,189	$	—	$	5	$	1,184
GSEs	212		—		1		211
Municipal securities	186		—		1		185
Asset-backed securities	63		—		—		63
U.S. treasury notes	78		—		—		78
Certificates of deposit	80		—		—		80
	$	1,808	$	—	$	7	$	1,801

Contractual maturities of investments

The contractual maturities of our investments as of September 30, 2016 are summarized below:

	Amortized Cost		Estimated Fair Value
	(In millions)
Due in one year or less	$	887	$	887
Due after one year through five years	817		821
Due after five years through ten years	26		27
	$	1,730	$	1,735

Schedule of available for sale securities continuous unrealized loss position

The following table segregates those available-for-sale investments that have been in a continuous loss position for less than 12 months, and those that have been in a loss position for 12 months or more as of December 31, 2015:

	In a Continuous Loss Position for Less than 12 Months					In a Continuous Loss Position for 12 Months or More
	Estimated Fair Value		Unrealized Losses		Total Number of Positions	Estimated Fair Value		Unrealized Losses		Total Number of Positions
	(Dollars in millions)
Corporate debt securities	$	825	$	4	588	$	119	$	1	87
GSEs	182		1		77	—		—		—
Municipal securities	128		1		181	—		—		—
	$	1,135	$	6	846	$	119	$	1	87