Pension and Postretirement Benefit Plans - Change in Benefit Obligation and Plan Assets and Amounts Recognized in Balance Sheet and AOCI (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Amounts recognized in the Consolidated Balance Sheet
Non-current assets	$ 230	$ 230	$ 208
Accrued benefit cost
Current liabilities	(67)	(67)	(76)
Non-current liabilities	(3,911)	(3,911)	(2,987)
Funded | Qualified and Non-qualified Pension Benefits
Change in benefit obligation
Settlements, curtailments, special termination benefits and other	32
Change in plan assets
Company contributions		207	366
Funded | Postretirement Benefits
Change in benefit obligation
Benefit obligation at beginning of year		2,175	2,410
Service cost		43	52	$ 52
Interest cost		82	79	80
Foreign exchange rate changes			(13)
Plan amendments		(171)
Actuarial (gain) loss		225	(244)
Benefit payments		(112)	(109)
Benefit obligation at end of year	2,242	2,242	2,175	2,410
Change in plan assets
Fair value, beginning balance		1,260	1,397
Actual return on plan assets		187	(32)
Company contributions		3	4
Benefit payments		(112)	(109)
Fair value, ending balance	1,338	1,338	1,260	1,397
Funded status at end of year	(904)	(904)	(915)
Accrued benefit cost
Current liabilities	(4)	(4)	(3)
Non-current liabilities	(900)	(900)	(912)
Ending balance	(904)	(904)	(915)
Amounts recognized in accumulated other comprehensive income
Net actuarial loss (gain)	663	663	584
Prior service cost (credit)	(262)	(262)	(123)
Ending balance	401	401	461
Funded | United States | Qualified and Non-qualified Pension Benefits
Change in benefit obligation
Benefit obligation at beginning of year		15,948	17,360
Service cost		251	288	268
Interest cost		620	563	565
Actuarial (gain) loss		2,209	(1,226)
Benefit payments		(1,128)	(1,034)
Settlements, curtailments, special termination benefits and other	32	35	(3)
Benefit obligation at end of year	17,935	17,935	15,948	17,360
Change in plan assets
Fair value, beginning balance		14,803	15,686
Acquisitions/Transfers			(4)
Actual return on plan assets		2,323	(95)
Company contributions		101	254
Benefit payments		(1,128)	(1,034)
Settlements, curtailments, special termination benefits and other			(4)
Fair value, ending balance	16,099	16,099	14,803	15,686
Funded status at end of year	(1,836)	(1,836)	(1,145)
Accrued benefit cost
Current liabilities	(48)	(48)	(60)
Non-current liabilities	(1,788)	(1,788)	(1,085)
Ending balance	(1,836)	(1,836)	(1,145)
Amounts recognized in accumulated other comprehensive income
Net actuarial loss (gain)	5,899	5,899	5,374
Prior service cost (credit)	(128)	(128)	(152)
Ending balance	5,771	5,771	5,222
Accumulated benefit obligations in excess of plan assets
Projected benefit obligation	17,935	17,935	593
Accumulated benefit obligation	17,125	17,125	521
Fair value of plan assets	16,099	16,099	9
Total Accumulated Benefit Obligation	17,125	17,125	15,033
Funded | International | Qualified and Non-qualified Pension Benefits
Change in benefit obligation
Benefit obligation at beginning of year		6,965	7,502
Acquisitions/Transfers		9	(11)
Service cost		131	143	142
Interest cost		156	157	157
Participant contributions		7	9
Foreign exchange rate changes		55	(387)
Plan amendments		3	7
Actuarial (gain) loss		906	(144)
Benefit payments		(302)	(304)
Settlements, curtailments, special termination benefits and other		1	(7)
Benefit obligation at end of year	7,931	7,931	6,965	7,502
Change in plan assets
Fair value, beginning balance		6,170	6,737
Acquisitions/Transfers		4
Actual return on plan assets		858	(38)
Company contributions		106	112
Participant contributions		7	9
Foreign exchange rate changes		80	(346)
Benefit payments		(302)	(304)
Fair value, ending balance	6,923	6,923	6,170	$ 6,737
Funded status at end of year	(1,008)	(1,008)	(795)
Amounts recognized in the Consolidated Balance Sheet
Non-current assets	230	230	208
Accrued benefit cost
Current liabilities	(15)	(15)	(13)
Non-current liabilities	(1,223)	(1,223)	(990)
Ending balance	(1,008)	(1,008)	(795)
Amounts recognized in accumulated other comprehensive income
Net transition obligation (asset)	10	10
Net actuarial loss (gain)	1,967	1,967	1,713
Prior service cost (credit)	(5)	(5)	(20)
Ending balance	1,972	1,972	1,693
Accumulated benefit obligations in excess of plan assets
Projected benefit obligation	2,986	2,986	2,613
Accumulated benefit obligation	2,752	2,752	2,415
Fair value of plan assets	1,778	1,778	1,633
Total Accumulated Benefit Obligation	$ 7,355	$ 7,355	$ 6,438