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, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in Fair Value of Plan Assets, Level 3 Reconciliation
Beginning balance	$ 604	$ 663	$ 525
Actual return on plan assets, relating to assets still held at the reporting date	85	(32)	50
Purchases	30	8	136
Sales	(61)	(35)	(48)
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Assets Transferred into (out of) Level 3	(137)
Ending balance	521	604	663
Alternative investments
Change in Fair Value of Plan Assets, Level 3 Reconciliation
Beginning balance	189	221	114
Actual return on plan assets, relating to assets still held at the reporting date	28	(10)	20
Purchases	24	0	126
Sales	(52)	(22)	(39)
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Assets Transferred into (out of) Level 3	(137)
Ending balance	52	189	221
Insurance Company Contracts [Member]
Change in Fair Value of Plan Assets, Level 3 Reconciliation
Beginning balance	166	173	173
Actual return on plan assets, relating to assets still held at the reporting date	12	(7)	(1)
Purchases	6	8	10
Sales	(9)	(8)	(9)
Ending balance	175	166	173
Life Insurance Contracts [Member]
Change in Fair Value of Plan Assets, Level 3 Reconciliation
Beginning balance	249	269	238
Actual return on plan assets, relating to assets still held at the reporting date	45	(15)	31
Purchases	0	0	0
Sales	0	(5)	0
Ending balance	$ 294	$ 249	$ 269