Financial Instruments and Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2018

Investments, Debt and Equity Securities [Abstract]

Summary of Financial Instruments by Significant Categories and Fair Value Measurement on a Recurring Basis

The following table summarizes our financial instruments by significant categories and fair value measurement on a recurring basis as of June 30, 2018 and December 31, 2017.

(in millions)	Level 1		Level 2		Total
June 30, 2018
Cash equivalents:
Money market funds	$	1	$	—	$	1
U.S. treasuries	—		7		7
Total cash equivalents	1		7		8
Investments:
Asset-backed securities	—		38		38
Corporate bonds	—		87		87
U.S. government agencies and government-sponsored agencies	—		6		6
U.S. treasuries	—		20		20
Other debt securities	—		11		11
Total investments	—		162		162
Restricted cash equivalents:
Money market mutual funds	229		—		229
Commercial paper	21		—		21
Total restricted cash equivalents	250		—		250
Restricted investments:
U.S. treasuries	—		14		14
Exchange traded fund	1		—		1
Certificate of deposit	—		2		2
Total restricted investments	1		16		17
Total investments and restricted cash equivalents and investments	$	252	$	185	$	437
December 31, 2017
Restricted cash equivalents:
Money market mutual funds	$	199	$	—	$	199
Commercial paper	21		—		21
Total restricted cash equivalents	220		—		220
Restricted investments:
U.S. treasuries	37		—		37
Exchange traded fund	1		—		1
Certificate of deposit	—		2		2
Total restricted investments	38		2		40
Total restricted cash equivalents and investments	$	258	$	2	$	260