Retirement Plans (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Capitalization of pension and OPEB expense related to engineering and plant construction	$ 24	$ 26	$ 26
Contribution of Property		37
Increase in plan assets	$ 382
Percentage of increase in pension plan	16.00%
Defined benefit plan, cash contributions by employer	$ 166
Accumulated benefit obligation	3,646	3,106
401(k) savings plan employer contributions	44	45	48
Plan assets	2,730	$ 2,348
Benefit payments	300
Investment returns	516
Special termination benefits	$ 44		$ 5
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate - used at year end to value obligation (in hundredths)	3.40%	4.30%	3.70%
Expected long-term rate of return on plan assets (in hundredths)	7.50%	7.50%	7.50%
Expected Long Term Rate Of Return On Plan Assets In Future Year In Hundredths	7.50%
Expected amortization of unrecognized loss	$ 70
Defined Benefit Plan, Settlements, Benefit Obligation	235	$ 254
Defined Benefit Plan, Settlements Benefit obligation threshold	212
Pension settlement costs	57	41	$ 83
Contribution of Property		37
Contributions to plans	$ 166	150
Contributions to plan, net of differential			75
Employer cash contributions		113
Defined Benefit Plan, Funded Percentage	73.00%
Differential Payment Received			131
Actuarial (gain) loss	$ 603	(88)
Plan assets	2,730	2,348	2,674
Benefit payments	65	63
Investment returns	(516)	159
Special termination benefits	38		$ 5
Postretirement Benefits Other Than Pensions (OPEB) [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected amortization of prior service credit	(32)
Expected amortization of unrecognized loss	(5)
Contributions to plans	$ 40	31
Percentage of increased medical cost trend rates	1.00%
Percentage of decreased medical cost trend rates	1.00%
Increase (decrease) in accumulated benefit obligation for plan amendment	$ 149
Actuarial (gain) loss	$ 129	(79)
Annual rate of increase in the per-capita cost of covered medical benefits (in hundredths)	6.50%
Annual rate of increase in the per-capita cost of covered medical benefits in 2025 (in hundredths)	5.00%
Effect on total of service and interest cost components, 1 percentage point increase	$ 1
Effect on postretirement benefit obligation, 1 percentage point increase	18
Effect on total of service and interest cost components, 1 percentage point decrease	(1)
Effect on postretirement benefit obligation, 1 percentage point decrease	(19)
Benefit payments	47	$ 38
Special termination benefits	$ 6
Postretirement Benefits Other Than Pensions (OPEB) [Member] | Minimum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate - used at year end to value obligation (in hundredths)	3.40%	4.30%	3.70%
Postretirement Benefits Other Than Pensions (OPEB) [Member] | Maximum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate - used at year end to value obligation (in hundredths)	3.50%	4.40%	3.80%
Fixed Income Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target asset allocation	40.00%
Equity [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target asset allocation	60.00%