Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2016

Fair value of assets measured on recurring basis

Our financial instruments measured at fair value on a recurring basis at September 30, 2016, were as follows:



	Total		Level 1		Level 2		Level 3
	(In millions)
Corporate debt securities	$	1,127	$	—	$	1,127	$	—
Government-sponsored enterprise securities (GSEs)	259		259		—		—
Municipal securities	148		—		148		—
Asset-backed securities	76		—		76		—
U.S. treasury notes	65		65		—		—
Certificates of deposit	60		—		60		—
Subtotal - current investments	1,735		324		1,411		—
1.125% Call Option derivative asset	314		—		—		314
Total assets measured at fair value on a recurring basis	$	2,049	$	324	$	1,411	$	314

1.125% Conversion Option derivative liability	$	314	$	—	$	—	$	314
Total liabilities measured at fair value on a recurring basis	$	314	$	—	$	—	$	314

Our financial instruments measured at fair value on a recurring basis at December 31, 2015, were as follows:



	Total		Level 1		Level 2		Level 3
	(In millions)
Corporate debt securities	$	1,184	$	—	$	1,184	$	—
GSEs	211		211		—		—
Municipal securities	185		—		185		—
Asset-backed securities	63		—		63		—
U.S. treasury notes	78		78		—		—
Certificates of deposit	80		—		80		—
Subtotal - current investments	1,801		289		1,512		—
1.125% Call Option derivative asset	374		—		—		374
Total assets measured at fair value on a recurring basis	$	2,175	$	289	$	1,512	$	374

1.125% Conversion Option derivative liability	$	374	$	—	$	—	$	374
Total liabilities measured at fair value on a recurring basis	$	374	$	—	$	—	$	374

Schedule of fair value, asset and liabilities measured on recurring basis - disclosure only

The carrying amounts and estimated fair values of our senior notes, which are classified as Level 2 financial instruments, are indicated in the following table.



	September 30, 2016				December 31, 2015
	Carrying Value		Fair Value		Carrying Value		Fair Value
	(In millions)
5.375% Notes	$	690	$	725	$	689	$	700
1.125% Convertible Notes	466		827		448		865
1.625% Convertible Notes	281		358		273		365
	$	1,437	$	1,910	$	1,410	$	1,930