Investments (Tables)

3 Months Ended

Mar. 31, 2016

Investments, Debt and Equity Securities [Abstract]

Investments

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

	March 31, 2016
	Amortized		Gross Unrealized				Estimated Fair
	Cost		Gains		Losses		Value
	(In millions)
Corporate debt securities	$	1,424	$	3	$	2	$	1,425
GSEs	214		—		—		214
Municipal securities	164		1		—		165
U.S. treasury notes	114		—		—		114
Certificates of deposit	78		—		—		78
Asset-backed securities	74		—		—		74
	$	2,068	$	4	$	2	$	2,070

	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
U.S. treasury notes	78		—		—		78
Certificates of deposit	80		—		—		80
Asset-backed securities	63		—		—		63
	$	1,808	$	—	$	7	$	1,801

Contractual maturities of investments

The contractual maturities of our investments as of March 31, 2016 are summarized below:

	Amortized Cost		Estimated Fair Value
	(In millions)
Due in one year or less	$	1,109	$	1,109
Due after one year through five years	938		940
Due after five years through ten years	21		21
	$	2,068	$	2,070

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 March 31, 2016:

	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	$	453	$	2	274	$	—	$	—	—

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