Retirement Benefits (Reconciliation Of The Beginning And Ending Balances Of Plan Assets Measured At Fair Value Using Level III Inputs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Change in Fair Value of Plan Assets, Level 3 Reconciliation
Beginning balance	$ 663	$ 525	$ 523
Actual return on plan assets, relating to assets still held at the reporting date	(32)	50	4
Purchases	8	136	27
Sales	(35)	(48)	(29)
Ending balance	604	663	525
Partnership Interests [Member]
Change in Fair Value of Plan Assets, Level 3 Reconciliation
Beginning balance	221	114	119
Actual return on plan assets, relating to assets still held at the reporting date	(10)	20	(4)
Purchases	0	126	18
Sales	(22)	(39)	(19)
Ending balance	189	221	114
Insurance Company Contracts [Member]
Change in Fair Value of Plan Assets, Level 3 Reconciliation
Beginning balance	173	173	174
Actual return on plan assets, relating to assets still held at the reporting date	(7)	(1)	(3)
Purchases	8	10	9
Sales	(8)	(9)	(7)
Ending balance	166	173	173
Life Insurance Contracts [Member]
Change in Fair Value of Plan Assets, Level 3 Reconciliation
Beginning balance	269	238	230
Actual return on plan assets, relating to assets still held at the reporting date	(15)	31	11
Purchases	0	0	0
Sales	(5)	0	(3)
Ending balance	$ 249	$ 269	$ 238