Retirement Benefits and Trusteed Assets (Pension Plan - Pension Cost Inclusions) (Details) - Pension plan - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 57	$ 95	$ 108
Interest cost	214	166	158
Expected return on plan assets	(352)	(346)	(339)
Amortization of:
Net actuarial loss	7	115	196
Prior service credit	(2)	(1)	0
Settlements	7	94	16
Net pension/other postretirement cost (credit)	$ (69)	$ 123	$ 139