Marketable Securities (Tables)

3 Months Ended

Mar. 31, 2019

Investments, Debt and Equity Securities [Abstract]

Schedule of Marketable Securities [Table Text Block]

	March 31, 2019						December 31, 2018
	Cost		Unrealized Gain (Loss)		Fair Value		Cost		Unrealized Gain (Loss)		Fair Value
U.S. government securities	$	2	$	—	$	2	$	2	$	—	$	2
Corporate securities	4				4		4				4
Certificates of deposit	14				14		15				15
Total marketable securities	$	20	$	—	$	20	$	21	$	—	$	21