Retirement Benefits (Net Amounts Included In Accumulated Other Comprehensive Loss That Have Not Been Recognized As Components Of Net Periodic Benefit Costs) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	$ 749	$ 734
Prior service cost (credit)	0	1
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	749	734
Prior service cost (credit)	0	1
Net amount before tax at December 31	749	735
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	3	25
Prior service cost (credit)	(12)	(19)
Net amount before tax at December 31	$ (9)	$ 6