Retirement Benefits - Status (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Plan
Plan Contributions [Abstract]
Payment for Pension and Other Postretirement Benefits	$ 570
Pension and Other Postretirement Benefit Contributions Unfunded Plans	360
Pension And Other Postretirement Expected Benefit Contributions Unfunded Plans	390
Pension Plan | Minimum
Plan Contributions [Abstract]
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year	600
Pension Plan | Maximum
Plan Contributions [Abstract]
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year	800
Pension Plan | U.S. Plans
Change in Benefit Obligation
Benefit obligation at January 1	45,672	$ 42,269
Service cost	520	474	$ 544
Interest cost	1,291	1,570	1,466
Amendments	0	0
Separation programs/other	(10)	(24)
Curtailments	0	0
Settlements	(25)	(966)
Plan participant contributions	23	23
Benefits paid	(3,055)	(2,615)
Foreign exchange translation	0	0
Actuarial (gain)/loss	4,604	4,941
Benefit obligation at December 31	49,020	45,672	42,269
Change in Plan Assets
Fair value of plan assets at January 1	44,253	39,774
Actual return on plan assets	7,018	7,800
Company contributions	186	284
Plan participant contributions	23	23
Benefits paid	(3,055)	(2,615)
Settlements	(25)	(966)
Foreign exchange translation	0	0
Defined Benefit Plan Other Increase Decrease Plan Assets	(45)	(47)
Fair value of plan assets at December 31	48,355	44,253	39,774
Funded status at December 31	(665)	(1,419)
Amounts Recognized on the Balance Sheet
Prepaid assets	1,578	911
Accrued liabilities	(2,243)	(2,330)
Total	(665)	(1,419)
Amounts Recognized in Accumulated Other Comprehensive Loss (pre-tax)
Unamortized prior service costs/(credits)	4	8
Pension Plans in which Accumulated Benefit Obligation Exceeds Plan Assets at December 31
Accumulated benefit obligation	2,295	2,141
Fair value of plan assets	145	156
Accumulated Benefit Obligation at December 31	47,848	44,578
Pension Plans in which Projected Benefit Obligation Exceeds Plan Assets at December 31
Projected benefit obligation	2,389	22,085
Fair value of plan assets	145	19,755
Expected Future Benefit Payments and Amortization
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	3,430
Defined Benefit Plan, Expected Future Benefit Payment, Year Two	2,750
Defined Benefit Plan, Expected Future Benefit Payment, Year Three	2,760
Defined Benefit Plan, Expected Future Benefit Payment, Year Four	2,790
Defined Benefit Plan, Expected Future Benefit Payment, Year Five	2,780
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Year Thereafter	13,730
Pension Plan | U.S. Plans | Alternatives
Change in Plan Assets
Fair value of plan assets at January 1	6,038
Fair value of plan assets at December 31	6,337	6,038
Pension Plan | U.S. Plans | Hedge Funds
Change in Plan Assets
Fair value of plan assets at January 1	2,961
Fair value of plan assets at December 31	3,258	2,961
Pension Plan | U.S. Plans | Private Equity Funds
Change in Plan Assets
Fair value of plan assets at January 1	1,884
Fair value of plan assets at December 31	1,859	1,884
Pension Plan | Non-U.S. Plans
Change in Benefit Obligation
Benefit obligation at January 1	35,373	31,079
Service cost	529	506	588
Interest cost	514	691	684
Amendments	0	10
Separation programs/other	219	391
Curtailments	0	(43)
Settlements	(189)	(272)
Plan participant contributions	14	17
Benefits paid	(1,394)	(1,395)
Foreign exchange translation	1,131	501
Actuarial (gain)/loss	3,638	3,888
Benefit obligation at December 31	39,835	35,373	31,079
Change in Plan Assets
Fair value of plan assets at January 1	29,958	27,273
Actual return on plan assets	4,149	2,935
Company contributions	744	789
Plan participant contributions	14	17
Benefits paid	(1,394)	(1,395)
Settlements	(189)	(330)
Foreign exchange translation	547	678
Defined Benefit Plan Other Increase Decrease Plan Assets	(9)	(9)
Fair value of plan assets at December 31	33,820	29,958	27,273
Funded status at December 31	(6,015)	(5,415)
Amounts Recognized on the Balance Sheet
Prepaid assets	2,673	2,318
Accrued liabilities	(8,688)	(7,733)
Total	(6,015)	(5,415)
Amounts Recognized in Accumulated Other Comprehensive Loss (pre-tax)
Unamortized prior service costs/(credits)	206	274
Pension Plans in which Accumulated Benefit Obligation Exceeds Plan Assets at December 31
Accumulated benefit obligation	14,595	12,421
Fair value of plan assets	7,203	5,948
Accumulated Benefit Obligation at December 31	36,272	32,106
Pension Plans in which Projected Benefit Obligation Exceeds Plan Assets at December 31
Projected benefit obligation	15,951	13,864
Fair value of plan assets	7,264	6,131
Expected Future Benefit Payments and Amortization
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	1,480
Defined Benefit Plan, Expected Future Benefit Payment, Year Two	1,360
Defined Benefit Plan, Expected Future Benefit Payment, Year Three	1,370
Defined Benefit Plan, Expected Future Benefit Payment, Year Four	1,380
Defined Benefit Plan, Expected Future Benefit Payment, Year Five	1,400
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Year Thereafter	7,210
Pension Plan | Non-U.S. Plans | Alternatives
Change in Plan Assets
Fair value of plan assets at January 1	2,227
Fair value of plan assets at December 31	2,311	2,227
Pension Plan | Non-U.S. Plans | Hedge Funds
Change in Plan Assets
Fair value of plan assets at January 1	1,207
Fair value of plan assets at December 31	1,259	1,207
Pension Plan | Non-U.S. Plans | Private Equity Funds
Change in Plan Assets
Fair value of plan assets at January 1	695
Fair value of plan assets at December 31	729	695
Worldwide OPEB
Change in Benefit Obligation
Benefit obligation at January 1	6,072	5,559
Service cost	47	43	54
Interest cost	169	211	195
Amendments	21	0
Separation programs/other	0	3
Curtailments	0	0
Settlements	0	0
Plan participant contributions	21	3
Benefits paid	(339)	(367)
Foreign exchange translation	28	69
Actuarial (gain)/loss	556	551
Benefit obligation at December 31	6,575	6,072	5,559
Change in Plan Assets
Fair value of plan assets at January 1	0	0
Actual return on plan assets	0	0
Company contributions	0	0
Plan participant contributions - Worldwide OPEB	0	0
Benefits paid - Worldwide OPEB	0	0
Settlements	0	0
Foreign exchange translation	0	0
Defined Benefit Plan Other Increase Decrease Plan Assets	0	0
Fair value of plan assets at December 31	0	0	$ 0
Funded status at December 31	(6,575)	(6,072)
Amounts Recognized on the Balance Sheet
Prepaid assets	0	0
Accrued liabilities	(6,575)	(6,072)
Total	(6,575)	(6,072)
Amounts Recognized in Accumulated Other Comprehensive Loss (pre-tax)
Unamortized prior service costs/(credits)	(11)	$ 29
Expected Future Benefit Payments and Amortization
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	340
Defined Benefit Plan, Expected Future Benefit Payment, Year Two	340
Defined Benefit Plan, Expected Future Benefit Payment, Year Three	330
Defined Benefit Plan, Expected Future Benefit Payment, Year Four	330
Defined Benefit Plan, Expected Future Benefit Payment, Year Five	330
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Year Thereafter	$ 1,640