Retirement Benefits (Funded Status Of Benefit Plans And Amounts Included In Regulatory Assets And OCI) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in plan assets:
Funded status – deficiency (surplus)	$ (216)	$ (481)
Amounts recognized in the balance sheet consist of:
Noncurrent liability	401	558
Net liability (asset) recognized	(216)	(481)
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation at end of year	4,735	4,258
Change in benefit obligation:
Net benefit obligation at beginning of year	4,459	4,827
Service cost	88	100	$ 93
Interest cost	187	169	179
Plan amendments	0	0
Participant contributions	0	0
Actuarial (gain) loss	469	(401)
Benefits paid	(236)	(236)
Net benefit obligation at end of year	4,967	4,459	4,827
Change in plan assets:
Fair value of plan assets at beginning of year	3,899	4,293
Actual return on plan assets	878	(218)
Employer contributions	23	60	64
Participant contributions	0	0
Benefits paid	(236)	(236)
Fair value of plan assets at end of year	4,564	3,899	4,293
Funded status – deficiency (surplus)	403	560
Accrued benefit cost (asset) at December 31	403	560
Amounts recognized in the balance sheet consist of:
Noncurrent asset(b)	0	0
Current liability(c)	2	2
Noncurrent liability	401	558
Net liability (asset) recognized	(403)	(560)
Amounts recognized in regulatory assets consist of:
Net actuarial (gain) loss	244	393
Prior service credit	0	(2)
Amounts recognized in accumulated OCI (pretax) consist of:
Net actuarial loss	26	35
Total	270	426
Postretirement Benefits
Change in benefit obligation:
Net benefit obligation at beginning of year	1,034	1,240
Service cost	18	21	21
Interest cost	43	40	47
Plan amendments	2	(49)
Participant contributions	8	9
Actuarial (gain) loss	69	(163)
Benefits paid	(64)	(64)
Net benefit obligation at end of year	1,110	1,034	1,240
Change in plan assets:
Fair value of plan assets at beginning of year	1,113	1,223
Actual return on plan assets	237	(57)
Employer contributions	3	2	2
Participant contributions	8	9
Benefits paid	(64)	(64)
Fair value of plan assets at end of year	1,297	1,113	$ 1,223
Funded status – deficiency (surplus)	(187)	(79)
Accrued benefit cost (asset) at December 31	(187)	(79)
Amounts recognized in the balance sheet consist of:
Noncurrent asset(b)	(187)	(79)
Current liability(c)	0	0
Noncurrent liability	0	0
Amounts recognized in regulatory assets consist of:
Net actuarial (gain) loss	(170)	(91)
Prior service credit	(41)	(48)
Amounts recognized in accumulated OCI (pretax) consist of:
Net actuarial loss	4	3
Total	$ (207)	$ (136)