Marketable Securities

9 Months Ended

Sep. 30, 2017

Investments, Debt and Equity Securities [Abstract]

Marketable Securities

Marketable Securities

	Cost		Unrealized Gains		Unrealized Losses		Fair Value
	(In millions)
September 30, 2017
United States government obligations
Maturity less than 1 year	$	259	$	—	$	—	$	259
Maturity 1 to 5 years	117		—		—		117
Corporate debt securities
Maturity less than 1 year	2		—		—		2
Maturity 1 to 5 years	90		—		—		90
	$	468	$	—	$	—	$	468

	Cost		Unrealized Gains		Unrealized Losses			Fair Value
	(In millions)
December 31, 2016
United States government obligations
Maturity less than 1 year	$	287	$	—	$	—		$	287
Maturity 1 to 5 years	121		—		(1		)	120
Corporate debt securities
Maturity less than 1 year	1		—		—			1
Maturity 1 to 5 years	66		—		—			66
Other debt securities
Maturity less than 1 year	8		—		—			8
Equity securities
Available-for-sale	1		—		—			1
	$	484	$	—	$	(1	)	$	483