Retirement Benefits - Calculation of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Amortization of:
Non-service net periodic benefit cost	$ (1)	$ 16	$ (2)	$ 33
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	38	58	77	119
Interest cost	144	110	289	220
Expected return on assets	(188)	(205)	(377)	(414)
Amortization of:
Prior service cost (credit)	0	1	1	2
Actuarial loss (gain)	43	73	84	149
Non-service net periodic benefit cost	37	37	74	76
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	6	10	12	20
Interest cost	26	19	51	38
Expected return on assets	(21)	(25)	(42)	(50)
Amortization of:
Prior service cost (credit)	(3)	(5)	(5)	(10)
Actuarial loss (gain)	(1)	4	(1)	8
Non-service net periodic benefit cost	$ 7	$ 3	$ 15	$ 6