Retirement Benefits and Trusteed Assets (Pension Plan - Pension Cost Inclusions) (Details) - Pension plan - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 84	$ 99	$ 92
Interest cost	219	202	214
Expected return on plan assets	(325)	(329)	(311)
Amortization of:
Net actuarial loss	133	176	176
Prior service cost	1	0	1
Net pension cost/other postretirement cost (credit)	$ 112	$ 148	$ 172