Retirement Benefits - Calculation of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Amortization of:
Non-service net periodic benefit cost	$ (7)	$ (1)
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	42	39
Interest cost	141	145
Expected return on assets	(184)	(189)
Amortization of:
Prior service cost (credit)	1	1
Actuarial loss	53	41
Non-service net periodic benefit cost	53	37
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	7	6
Interest cost	24	25
Expected return on assets	(21)	(21)
Amortization of:
Prior service cost (credit)	(2)	(2)
Actuarial loss	0	0
Non-service net periodic benefit cost	$ 8	$ 8