Marketable Securities
 3 Months Ended
Mar. 31, 2018
Investments, Debt and Equity Securities [Abstract]  
Marketable Securities [Text Block]
Marketable Securities 
 
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


 
U.S. government securities include bonds issued by government-sponsored agencies and Treasury notes. Corporate securities are primarily debt securities. Other consists of investments in mutual and index funds. U.S. government securities, corporate debt and certificates of deposit maturing in one year or less, after one year through five years and after five years through ten years total $29, $4 and $3 at March 31, 2018.