Retirement Benefits - Calculation of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Amortization of:
Non-service net periodic benefit cost	$ (1)	$ 17
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	39	61
Interest cost	145	110
Expected return on assets	(189)	(209)
Amortization of:
Prior service cost (credit)	1	1
Actuarial loss	41	76
Non-service net periodic benefit cost	37	39
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	6	10
Interest cost	25	19
Expected return on assets	(21)	(25)
Amortization of:
Prior service cost (credit)	(2)	(5)
Actuarial loss	0	4
Non-service net periodic benefit cost	$ 8	$ 3