Marketable Securities (Tables)

3 Months Ended

Mar. 31, 2018

Investments, Debt and Equity Securities [Abstract]

Schedule of Marketable Securities [Table Text Block]

	March 31, 2018						December 31, 2017
	Cost		Unrealized Gain (Loss)		Fair Value		Cost		Unrealized Gain (Loss)		Fair Value
U.S. government securities	$	3	$	—	$	3	$	3	$	—	$	3
Corporate securities	5				5		5				5
Certificates of deposit	28				28		27				27
Other	5				5		4		1		5
Total marketable securities	$	41	$	—	$	41	$	39	$	1	$	40