Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2018

Investments, Debt and Equity Securities [Abstract]

Schedule of Marketable Securities [Table Text Block]

	2018						2017
	Cost		Unrealized Gains (Losses)		Fair Value		Cost		Unrealized Gains (Losses)		Fair Value
U.S. government securities	$	2	$	—	$	2	$	3	$	—	$	3
Corporate securities	4				4		5				5
Certificates of deposit	15				15		27				27
Other							4		1		5
Total marketable securities	$	21	$	—	$	21	$	39	$	1	$	40