Marketable Securities - Schedule of Marketable Securities (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 37	$ 39
Unrealized Gain (Loss)	0	1
Fair Value	37	40
US Treasury and Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	3	3
Unrealized Gain (Loss)	0	0
Fair Value	3	3
Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	5	5
Unrealized Gain (Loss)
Fair Value	5	5
Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	24	27
Unrealized Gain (Loss)
Fair Value	24	27
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	5	4
Unrealized Gain (Loss)		1
Fair Value	$ 5	$ 5