Commitments and Contingencies, Asset Retirement Obligations (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	$ 2,475	$ 2,782
Liabilities Incurred	13	1
Liabilities Settled	(14)	(30)
Accretion	120	136
Cash flow revisions	(26)	(414)
Ending balance	2,568	2,475
Legally restricted assets, for purposes of funding future nuclear decommissioning	2,055
Electric Plant Nuclear Production Decommissioning
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	1,874	2,249
Liabilities Incurred	0	0
Liabilities Settled	0	0
Accretion	94	114
Cash flow revisions	0	(489)
Ending balance	1,968	1,874
Electric Plant Wind Production
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	96	92
Liabilities Incurred	12	0
Liabilities Settled	0	0
Accretion	4	4
Cash flow revisions	7	0
Ending balance	119	96
Electric Plant Steam, Hydro and Other Production Asbestos
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	192	205
Liabilities Incurred	0	1
Liabilities Settled	(14)	(29)
Accretion	8	9
Cash flow revisions	(9)	6
Ending balance	177	192
Electric Plant Electric Distribution
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	21	20
Liabilities Incurred	0	0
Liabilities Settled	0	0
Accretion	1	1
Cash flow revisions	20	0
Ending balance	42	21
Electric Plant Other
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	5	5
Liabilities Incurred	0	0
Liabilities Settled	0	0
Accretion	0	0
Cash flow revisions	2	0
Ending balance	7	5
Natural Gas Plant Gas Transmission and Distribution
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	282	205
Liabilities Incurred	0	0
Liabilities Settled	0	0
Accretion	13	8
Cash flow revisions	(46)	69
Ending balance	249	282
Natural Gas Plant Other
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	4	4
Liabilities Incurred	0	0
Liabilities Settled	0	0
Accretion	0	0
Cash flow revisions	0	0
Ending balance	4	4
Common and Other Property Common Miscellaneous
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	1	2
Liabilities Incurred	0	0
Liabilities Settled	0	(1)
Accretion	0	0
Cash flow revisions	0	0
Ending balance	1	1
Non utility and other
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	0
Liabilities Incurred	1
Liabilities Settled	0
Accretion	0
Cash flow revisions	0
Ending balance	$ 1	$ 0

The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

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Amount of accretion expense recognized during the period that is associated with an asset retirement obligation. Accretion expense measures and incorporates changes due to the passage of time into the carrying amount of the liability.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)(3)
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6392676&loc=d3e7480-110848

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Amount of asset retirement obligations incurred during the period.

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Amount of asset retirement obligations settled, or otherwise disposed of, during the period. This may include asset retirement obligations transferred to third parties associated with the sale of a long-lived asset.

+ References

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Amount of increase (decrease) in the asset retirement obligation from changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 35
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=6392603&loc=d3e7123-110846

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-Publisher FASB
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-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)(4)
-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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The fair value of investments held in a trust fund to pay for the costs of decontaminating and decommissioning facilities, whether such amount is presented as a separate caption or as a parenthetical disclosure on the balance sheet. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

+ References

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