Post-Employment Benefits - Benefit Plan Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair value of plan assets
Beginning of period	$ 5,399
End of period	5,637	$ 5,399
Amounts recognized on the consolidated balance sheets
Other long-term liabilities	(1,840)	(2,740)
Defined benefit plans
Projected benefit obligations
Beginning of period	6,985	5,829
Service cost	285	236	$ 210
Interest cost	227	204	201
Employee contributions	2	2
Actuarial (gain) loss	(614)	714
Benefits paid	(191)	(173)
Other, primarily foreign currency translation adjustments	(76)	173
End of period	6,618	6,985	5,829
Fair value of plan assets
Beginning of period	5,399	4,572
Actual return on plan assets	(384)	684
Company contributions	873	246
Employee contributions	2	2
Benefits paid	(191)	(173)
Other, primarily foreign currency translation adjustments	(62)	68
End of period	5,637	5,399	4,572
Funded status, end of period	(981)	(1,586)
Amounts recognized on the consolidated balance sheets
Other assets	321	388
Accounts payable and accrued liabilities	(8)	(32)
Other long-term liabilities	(1,294)	(1,942)
Net obligation	(981)	(1,586)
Actuarial loss, net	2,516	2,471
Prior service cost (credit)	11	12
Accumulated other comprehensive loss	2,527	2,483
Other post-employment plans
Projected benefit obligations
Beginning of period	813	627
Service cost	26	26	25
Interest cost	25	24	24
Actuarial (gain) loss	(287)	149
Benefits paid	(16)	(15)
Other, primarily foreign currency translation adjustments	0	2
End of period	561	813	$ 627
Fair value of plan assets
Company contributions	16	15
Benefits paid	(16)	(15)
Funded status, end of period	(561)	(813)
Amounts recognized on the consolidated balance sheets
Accounts payable and accrued liabilities	(15)	(15)
Other long-term liabilities	(546)	(798)
Net obligation	(561)	(813)
Actuarial loss, net	25	320
Prior service cost (credit)	(22)	(29)
Accumulated other comprehensive loss	$ 3	$ 291