Retirement Benefits (Funded Status Of Benefit Plans And Amounts Included In Regulatory Assets And OCI) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Change in plan assets:
Funded status – deficiency	$ (551)	$ (774)
Amounts recognized in the balance sheet consist of:
Noncurrent liability	545	769
Net liability recognized	551	774
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation at end of year	4,577	4,288
Change in benefit obligation:
Net benefit obligation at beginning of year	4,518	4,197
Service cost	93	81	$ 92
Interest cost	179	185	174
Actuarial loss	255	265
Benefits paid	(218)	(210)
Net benefit obligation at end of year	4,827	4,518	4,197
Change in plan assets:
Fair value of plan assets at beginning of year	3,813	3,653
Actual return on plan assets	634	313
Employer contributions	64	57	111
Benefits paid	(218)	(210)
Fair value of plan assets at end of year	4,293	3,813	3,653
Funded status – deficiency	534	705
Accrued benefit cost at December 31	534	705
Amounts recognized in the balance sheet consist of:
Current liability(c)	3	3
Noncurrent liability	531	702
Net liability recognized	534	705
Amounts recognized in regulatory assets consist of:
Net actuarial (gain) loss	374	535
Prior service credit	(3)	(4)
Amounts (pretax) recognized in accumulated OCI consist of:
Net actuarial loss	30	43
Prior service credit	0	0
Total	401	574
Postretirement Benefits
Change in benefit obligation:
Net benefit obligation at beginning of year	1,170	1,094
Service cost	21	19	24
Interest cost	47	50	48
Participant contributions	8	8
Actuarial loss	53	52
Benefits paid	(59)	(54)
Federal subsidy on benefits paid	0	1
Net benefit obligation at end of year	1,240	1,170	1,094
Change in plan assets:
Fair value of plan assets at beginning of year	1,101	1,071
Actual return on plan assets	171	73
Employer contributions	2	2	18
Federal subsidy on benefits paid	0	1
Participant contributions	8	8
Benefits paid	(59)	(54)
Fair value of plan assets at end of year	1,223	1,101	$ 1,071
Funded status – deficiency	17	69
Accrued benefit cost at December 31	17	69
Amounts recognized in the balance sheet consist of:
Current liability(c)	3	2
Noncurrent liability	14	67
Net liability recognized	17	69
Amounts recognized in regulatory assets consist of:
Net actuarial (gain) loss	(69)	(29)
Prior service credit	(3)	(8)
Amounts (pretax) recognized in accumulated OCI consist of:
Net actuarial loss	2	0
Prior service credit	0	(1)
Total	$ (70)	$ (38)