Retirement Plans (Net Periodic Pension And OPEB Cost) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net Periodic Pension And OPEB Cost [Abstract]
Curtailment cost			$ 20
Special termination cost			49
Pension [Member]
Net Periodic Pension And OPEB Cost [Abstract]
Service cost	$ 80	$ 105	90
Interest cost	160	145	142
Expected return on plan assets	(273)	(272)	(267)
Curtailment cost			20
Special termination cost			49
Amortization of prior service cost/(credit)
Amortization of actuarial loss	67	93	81
Net periodic pension/OPEB cost	34	71	115
OPEB [Member]
Net Periodic Pension And OPEB Cost [Abstract]
Service cost	1	2	2
Interest cost	9	10	10
Expected return on plan assets
Amortization of prior service cost/(credit)	(7)	1	1
Amortization of actuarial loss	7	10	9
Net periodic pension/OPEB cost	$ 10	$ 23	$ 22