Segment Information (Financial Data By Reportable Segment) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Reportable segments operating revenues	$ 22,980	$ 22,097	$ 68,037	$ 66,614
Operating gain (loss)	1,249	982	4,676	3,794
Commercial and Specialty Business [Member]
Segment Reporting Information [Line Items]
Reportable segments operating revenues	9,128	10,052	27,357	30,651
Operating gain (loss)	833	535	3,295	2,805
Government Business [Member]
Segment Reporting Information [Line Items]
Reportable segments operating revenues	13,841	12,037	40,647	35,946
Operating gain (loss)	466	457	1,494	1,069
Other [Member]
Segment Reporting Information [Line Items]
Reportable segments operating revenues	11	8	33	17
Operating gain (loss)	$ (50)	$ (10)	$ (113)	$ (80)