Financial Instruments and Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 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 March 31, 2018 and December 31, 2017.

(in millions)	Level 1		Level 2		Total
March 31, 2018
Restricted cash equivalents:
Money market mutual funds	$	224	$	—	$	224
Commercial paper	20		—		20
Total restricted cash equivalents	244		—		244
Restricted investments:
U.S. Treasuries	23		—		23
Exchange traded fund	1		—		1
Certificate of deposit	—		2		2
Total restricted investments	24		2		26
Total restricted cash equivalents and investments	$	268	$	2	$	270
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