Leased Facilities (Net Rental Cost) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Leased Assets [Line Items]
Rental cost	$ 2,715	$ 2,618	$ 3,091
Drilling Rigs and Related Equipment [Member]
Operating Leased Assets [Line Items]
Rental cost	723	792	1,274
Other [Member]
Operating Leased Assets [Line Items]
Rental cost	$ 1,992	$ 1,826	$ 1,817