Retirement Benefits - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Amortization of:
Non-service net periodic benefit cost	$ 63	$ 91	$ 53
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	236	294	251
Interest cost	439	406	476
Expected return on assets	(822)	(843)	(796)
Amortization of:
Prior service cost (credit)	2	2	3
Actuarial loss	295	399	349
Curtailment benefits	0	0	0
Settlement and other charges	0	7	6
Non-service net periodic benefit cost	150	265	289
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	41	51	56
Interest cost	76	69	93
Expected return on assets	(99)	(99)	(101)
Amortization of:
Prior service cost (credit)	(19)	(25)	(76)
Actuarial loss	12	27	34
Curtailment benefits	0	0	(1)
Settlement and other charges	0	1	1
Non-service net periodic benefit cost	$ 11	$ 24	$ 6