Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2018

Fair Value Disclosures [Abstract]

Financial Instruments Measured at Fair Value on a Recurring Basis

Financial instruments measured at fair value on a recurring basis as of June 30, 2018 and December 31, 2017 are as follows (in millions):

	As of June 30, 2018						As of December 31, 2017
	Level 1		Level 2 and 3		Total		Level 1		Level 2 and 3		Total
Assets at fair value:
U.S. Treasury and other foreign government securities	$	944	$	—	$	944	$	734	$	—	$	734
Mutual funds	15		—		15		16		—		16
Total assets at fair value	$	959	$	—	$	959	$	750	$	—	$	750