Quarterly Financial Data - Unaudited (Tables)

12 Months Ended

Dec. 31, 2018

Dec. 31, 2017

Quaterly Financial Data Unaudited [Abstract]

Schedule of Quarterly Financial Information [Table Text Block]

2018	Fourth		Third		Second		First
Revenues	$	6,206	$	6,147	$	5,878	$	5,624
Operating income	$	2,061	$	2,109	$	1,883	$	1,747
Net income	$	1,372	$	1,393	$	1,309	$	1,145

2017	Fourth		Third		Second		First
Revenues	$	5,638	$	5,314	$	5,250	$	5,185
Operating income	$	1,999	$	1,940	$	1,774	$	1,580
Net income	$	8,462	$	1,042	$	958	$	838