Retirement Benefits - Calculation of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Amortization of:
Non-service net periodic benefit cost	$ 17	$ 20
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	61	74
Interest cost	110	102
Expected return on assets	(209)	(213)
Amortization of:
Prior service cost (credit)	1	1
Actuarial loss	76	100
Curtailment benefits	0	0
Non-service net periodic benefit cost	39	64
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	10	14
Interest cost	19	17
Expected return on assets	(25)	(26)
Amortization of:
Prior service cost (credit)	(5)	(6)
Actuarial loss	4	7
Curtailment benefits	0	(1)
Non-service net periodic benefit cost	$ 3	$ 5