Retirement Benefits (Components Of Net Periodic (Benefit Credit) Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 12	$ 16
Expected return on assets	(40)	(34)
Recognized actuarial loss	6	4
Settlement loss	5	2
Amortization of prior service cost (credit)	0	0
Net periodic benefit credit	(17)	(12)
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	3	4
Expected return on assets	(6)	(5)
Recognized actuarial loss	0	0
Settlement loss	0	0
Amortization of prior service cost (credit)	(2)	(3)
Net periodic benefit credit	$ (5)	$ (4)