Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2017

Fair value of assets measured on recurring basis

Our financial instruments measured at fair value on a recurring basis at March 31, 2017, were as follows:



	Total		Level 1		Level 2		Level 3
	(In millions)
Corporate debt securities	$	1,353	$	—	$	1,353	$	—
Government-sponsored enterprise securities (GSEs)	209		209		—		—
U.S. treasury notes	193		193		—		—
Municipal securities	152		—		152		—
Asset-backed securities	110		—		110		—
Certificates of deposit	39		—		39		—
Subtotal - current investments	2,056		402		1,654		—
1.125% Call Option derivative asset	181		—		—		181
Total assets measured at fair value on a recurring basis	$	2,237	$	402	$	1,654	$	181

1.125% Conversion Option derivative liability	$	181	$	—	$	—	$	181
Total liabilities measured at fair value on a recurring basis	$	181	$	—	$	—	$	181

Our financial instruments measured at fair value on a recurring basis at December 31, 2016, were as follows:



	Total		Level 1		Level 2		Level 3
	(In millions)
Corporate debt securities	$	1,179	$	—	$	1,179	$	—
GSEs	231		231		—		—
U.S. treasury notes	84		84		—		—
Municipal securities	142		—		142		—
Asset-backed securities	69		—		69		—
Certificates of deposit	53		—		53		—
Subtotal - current investments	1,758		315		1,443		—
1.125% Call Option derivative asset	267		—		—		267
Total assets measured at fair value on a recurring basis	$	2,025	$	315	$	1,443	$	267

1.125% Conversion Option derivative liability	$	267	$	—	$	—	$	267
Total liabilities measured at fair value on a recurring basis	$	267	$	—	$	—	$	267

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.



	March 31, 2017				December 31, 2016
	Carrying Value		Fair Value		Carrying Value		Fair Value
	(In millions)
5.375% Notes	$	691	$	726	$	691	$	714
1.125% Convertible Notes	477		705		471		792
1.625% Convertible Notes	287		321		284		344
	$	1,455	$	1,752	$	1,446	$	1,850