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, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	$ 734	$ 751
Prior service cost (credit)	1	1
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	734	751
Prior service cost (credit)	1	1
Net amount before tax at December 31	735	752
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	25	58
Prior service cost (credit)	(19)	(34)
Net amount before tax at December 31	$ 6	$ 24