Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2017

Investments, Debt and Equity Securities [Abstract]

Summary of Marketable Securities [Table Text Block]

	2017						2016
	Cost		Unrealized Gains (Losses)		Fair Value		Cost		Unrealized Gains (Losses)		Fair Value
U.S. government securities	$	3	$	—	$	3	$	2	$	—	$	2
Corporate securities	5				5		2				2
Certificates of deposit	27				27		22				22
Other	4		1		5		4				4
Total marketable securities	$	39	$	1	$	40	$	30	$	—	$	30