Investments (Tables)

9 Months Ended

Sep. 30, 2021

Investments, Debt and Equity Securities [Abstract]

Investments

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

	September 30, 2021
	Amortized Cost		Gross Unrealized				Estimated Fair Value
			Gains		Losses
	(In millions)
Corporate debt securities	$	1,688	$	19	$	2	$	1,705
Mortgage-backed securities	607		4		1		610
U.S. Treasury notes	235		—		—		235
Asset-backed securities	223		1		—		224
Municipal securities	96		1		—		97
Other	29		—		—		29
Total	$	2,878	$	25	$	3	$	2,900

	December 31, 2020
	Amortized Cost		Gross Unrealized				Estimated Fair Value
			Gains		Losses
	(In millions)
Corporate debt securities	$	1,220	$	36	$	—	$	1,256
Mortgage-backed securities	383		10		1		392
U.S. Treasury notes	27		—		—		27
Asset-backed securities	130		2		—		132
Municipal securities	66		2		—		68
Total	$	1,826	$	50	$	1	$	1,875

Contractual maturities of investments

The contractual maturities of our available-for-sale investments as of September 30, 2021 are summarized below:

	Amortized Cost		Estimated Fair Value
	(In millions)
Due in one year or less	$	555	$	557
Due after one year through five years	1,530		1,546
Due after five years through ten years	296		298
Due after ten years	497		499
Total	$	2,878	$	2,900

Available-for-sale investments

The following table summarizes those available-for-sale investments that have been in a continuous loss position for less than 12 months. No investments have been in a continuous loss position for 12 months or more as of September 30, 2021, and December 31, 2020.

	September 30, 2021					December 31, 2020
	Estimated Fair Value		Unrealized Losses		Total Number of Positions	Estimated Fair Value		Unrealized Losses		Total Number of Positions
	(Dollars in millions)
Corporate debt securities	$	509	$	2	174	$	—	$	—	—
Mortgage-backed securities	270		1		94	77		1		21
Total	$	779	$	3	268	$	77	$	1	21