Business Segment Reporting (Components of FAS/CAS Operating Adjustment) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Operating income	$ 4,774	$ 4,538	$ 4,231
FAS/CAS Pension Operating Adjustment [Member]
Segment Reporting Information [Line Items]
Operating income	1,439	1,415	1,291
FAS/CAS PRB Operating Adjustment [Member]
Segment Reporting Information [Line Items]
Operating income	15	13	12
FAS/CAS Operating Adjustment [Member]
Segment Reporting Information [Line Items]
Operating income	$ 1,454	$ 1,428	$ 1,303