Retirement Benefits - Calculation of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Amortization of:
Non-service net periodic benefit cost	$ 16	$ 26	$ 33	$ 46
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	58	75	119	148
Interest cost	110	101	220	202
Expected return on assets	(205)	(210)	(414)	(421)
Amortization of:
Prior service cost (credit)	1	0	2	1
Actuarial loss	73	99	149	199
Curtailment benefits			0	0
Non-service net periodic benefit cost	37	65	76	129
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	10	13	20	26
Interest cost	19	17	38	35
Expected return on assets	(25)	(25)	(50)	(50)
Amortization of:
Prior service cost (credit)	(5)	(7)	(10)	(13)
Actuarial loss	4	8	8	14
Curtailment benefits			0	(1)
Non-service net periodic benefit cost	$ 3	$ 6	$ 6	$ 11