Retirement Benefits and Trusteed Assets (Pension Plan - Pension Cost Inclusions) (Details) - Pension plan - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 99	$ 92	$ 92
Interest cost	202	214	219
Expected return on plan assets	(329)	(311)	(309)
Amortization of:
Net actuarial loss	176	176	164
Prior service cost	0	1	1
Net pension cost/other postretirement credit	$ 148	$ 172	$ 167