Pension and Postretirement Benefit Plans - Change in Benefit Obligation and Plan Assets and Amounts Recognized in Balance Sheet and AOCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Amounts recognized in the Consolidated Balance Sheet
Non-current assets	$ 208	$ 237
Accrued benefit cost
Current liabilities	(76)	(69)
Non-current liabilities	(2,987)	(3,620)
Funded | Qualified and Non-qualified Pension Benefits
Change in plan assets
Company contributions	366	964
Funded | Postretirement Benefits
Change in benefit obligation
Benefit obligation at beginning of year	2,410	2,259
Service cost	52	52	$ 54
Interest cost	79	80	79
Foreign exchange rate changes	(13)	3
Plan amendments		(6)
Actuarial (gain) loss	(244)	127
Benefit payments	(109)	(105)
Benefit obligation at end of year	2,175	2,410	2,259
Change in plan assets
Fair value, beginning balance	1,397	1,356
Actual return on plan assets	(32)	143
Company contributions	4	3
Benefit payments	(109)	(105)
Fair value, ending balance	1,260	1,397	1,356
Funded status at end of year	(915)	(1,013)
Accrued benefit cost
Current liabilities	(3)	(4)
Non-current liabilities	(912)	(1,009)
Ending balance	(915)	(1,013)
Amounts recognized in accumulated other comprehensive income
Net actuarial loss (gain)	584	774
Prior service cost (credit)	(123)	(163)
Ending balance	461	611
Funded | United States | Qualified and Non-qualified Pension Benefits
Change in benefit obligation
Benefit obligation at beginning of year	17,360	16,202
Service cost	288	268	259
Interest cost	563	565	575
Actuarial (gain) loss	(1,226)	1,263
Benefit payments	(1,034)	(936)
Settlements, curtailments, special termination benefits and other	(3)	(2)
Benefit obligation at end of year	15,948	17,360	16,202
Change in plan assets
Fair value, beginning balance	15,686	14,081
Acquisitions/Transfers	(4)
Actual return on plan assets	(95)	1,693
Company contributions	254	852
Benefit payments	(1,034)	(936)
Settlements, curtailments, special termination benefits and other	(4)	(4)
Fair value, ending balance	14,803	15,686	14,081
Funded status at end of year	(1,145)	(1,674)
Amounts recognized in the Consolidated Balance Sheet
Non-current assets		4
Accrued benefit cost
Current liabilities	(60)	(53)
Non-current liabilities	(1,085)	(1,625)
Ending balance	(1,145)	(1,674)
Amounts recognized in accumulated other comprehensive income
Net actuarial loss (gain)	5,374	5,921
Prior service cost (credit)	(152)	(175)
Ending balance	5,222	5,746
Accumulated benefit obligations in excess of plan assets
Projected benefit obligation	593	17,350
Accumulated benefit obligation	521	16,260
Fair value of plan assets	9	15,671
Total Accumulated Benefit Obligation	15,033	16,270
Funded | International | Qualified and Non-qualified Pension Benefits
Change in benefit obligation
Benefit obligation at beginning of year	7,502	6,625
Acquisitions/Transfers	(11)	3
Service cost	143	142	133
Interest cost	157	157	171
Participant contributions	9	8
Foreign exchange rate changes	(387)	667
Plan amendments	7	6
Actuarial (gain) loss	(144)	170
Benefit payments	(304)	(276)
Settlements, curtailments, special termination benefits and other	(7)
Benefit obligation at end of year	6,965	7,502	6,625
Change in plan assets
Fair value, beginning balance	6,737	5,617
Acquisitions/Transfers		2
Actual return on plan assets	(38)	714
Company contributions	112	112
Participant contributions	9	8
Foreign exchange rate changes	(346)	560
Benefit payments	(304)	(276)
Fair value, ending balance	6,170	6,737	$ 5,617
Funded status at end of year	(795)	(765)
Amounts recognized in the Consolidated Balance Sheet
Non-current assets	208	233
Accrued benefit cost
Current liabilities	(13)	(12)
Non-current liabilities	(990)	(986)
Ending balance	(795)	(765)
Amounts recognized in accumulated other comprehensive income
Net actuarial loss (gain)	1,713	1,720
Prior service cost (credit)	(20)	(40)
Ending balance	1,693	1,680
Accumulated benefit obligations in excess of plan assets
Projected benefit obligation	2,613	2,687
Accumulated benefit obligation	2,415	2,449
Fair value of plan assets	1,633	1,731
Total Accumulated Benefit Obligation	$ 6,438	$ 6,870