Retirement Benefits - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Amortization of:
Net periodic benefit cost	$ (38)	$ (18)	$ 63
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	166	155	236
Interest cost	565	578	439
Expected return on assets	(736)	(755)	(822)
Amortization of:
Prior service cost (credit)	2	2	2
Actuarial loss (gain)	214	166	295
Settlement and other charges	10	20	0
Net periodic benefit cost	221	166	150
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	27	26	41
Interest cost	96	101	76
Expected return on assets	(84)	(83)	(99)
Amortization of:
Prior service cost (credit)	(8)	(10)	(19)
Actuarial loss (gain)	0	(2)	12
Settlement and other charges	0	0	0
Net periodic benefit cost	$ 31	$ 32	$ 11