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Nuclear Decommissioning Trust Fund - Summary of Aggregate Fair Values and Realized Gains and Losses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Nuclear decommissioning trust fund disclosure
Fair Value	$ 890	$ 794
Unrealized Gains	398	338
Unrealized Losses	0	1
Cash and cash equivalents
Nuclear decommissioning trust fund disclosure
Fair Value	23	17
Unrealized Gains	0	0
Unrealized Losses	0	0
U.S. government and federal agency obligations
Nuclear decommissioning trust fund disclosure
Fair Value	70	68
Unrealized Gains	6	4
Unrealized Losses	$ 0	$ 0
Weighted- average maturities (in years)	10 years	11 years
Federal agency mortgage-backed securities
Nuclear decommissioning trust fund disclosure
Fair Value	$ 89	$ 100
Unrealized Gains	4	3
Unrealized Losses	$ 0	$ 0
Weighted- average maturities (in years)	24 years	24 years
Commercial mortgage-backed securities
Nuclear decommissioning trust fund disclosure
Fair Value	$ 36	$ 29
Unrealized Gains	2	1
Unrealized Losses	$ 0	$ 1
Weighted- average maturities (in years)	27 years	24 years
Corporate debt securities
Nuclear decommissioning trust fund disclosure
Fair Value	$ 144	$ 109
Unrealized Gains	13	6
Unrealized Losses	$ 0	$ 0
Weighted- average maturities (in years)	12 years	11 years
Equity securities
Nuclear decommissioning trust fund disclosure
Fair Value	$ 521	$ 466
Unrealized Gains	372	324
Unrealized Losses	0	0
Foreign government fixed income securities
Nuclear decommissioning trust fund disclosure
Fair Value	7	5
Unrealized Gains	1	0
Unrealized Losses	$ 0	$ 0
Weighted- average maturities (in years)	10 years	10 years
South Texas Project
Nuclear decommissioning trust fund disclosure
Ownership Interest (as a percent)	44.00%

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Decommissioning Fund Investments, Unrealized Gains

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The weighted-average maturity period for securities of nuclear decommissioning trust funds assets.

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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

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 (b)
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The proportionate share of interest (percent) in a jointly owned utility plant.

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-Name Accounting Standards Codification
-Topic 980
-SubTopic 360
-Section S99
-Paragraph 1
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