Other Financial Data - Other Liabilities (Details) - USD ($) $ in Millions	1 Months Ended	6 Months Ended
	Feb. 28, 2018	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Other Liabilities [Abstract]
Defined benefit plans		$ 1,464		$ 2,019
Non-current contract liabilities (Note 2)		180	$ 162
Deferred revenue (Note 1)				169
Unrecognized tax benefits		52		54
Deferred income taxes		240		115
Other		217		228
Other liabilities		2,153	$ 2,578	$ 2,585
Pension Benefit Plan | U.S.
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan contributions	$ 500	$ 500