Retirement Benefits (Reconciliation Of The Beginning And Ending Balances Of Plan Assets Measured At Fair Value Using Level III Inputs) (Details) - Fair Value, Inputs, Level 3 [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in Fair Value of Plan Assets, Level 3 Reconciliation
Beginning balance	$ 469	$ 415	$ 442
Actual return on plan assets, relating to assets still held at the reporting date	36	57	(22)
Purchases	15	6	8
Sales	(8)	(9)	(13)
Ending balance	512	469	415
Insurance Company Contracts [Member]
Change in Fair Value of Plan Assets, Level 3 Reconciliation
Beginning balance	175	166	173
Actual return on plan assets, relating to assets still held at the reporting date	7	12	(7)
Purchases	15	6	8
Sales	(8)	(9)	(8)
Ending balance	189	175	166
Life Insurance Contracts [Member]
Change in Fair Value of Plan Assets, Level 3 Reconciliation
Beginning balance	294	249	269
Actual return on plan assets, relating to assets still held at the reporting date	29	45	(15)
Purchases	0	0	0
Sales	0	0	(5)
Ending balance	$ 323	$ 294	$ 249