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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, 2019	Dec. 31, 2018
Nuclear decommissioning trust fund disclosure
Fair Value	$ 794	$ 663
Unrealized Gains	338	234
Unrealized Losses	1	6
Cash and cash equivalents
Nuclear decommissioning trust fund disclosure
Fair Value	17	19
Unrealized Gains	0	0
Unrealized Losses	0	0
U.S. government and federal agency obligations
Nuclear decommissioning trust fund disclosure
Fair Value	68	46
Unrealized Gains	4	1
Unrealized Losses	$ 0	$ 0
Weighted- average maturities (in years)	11 years	12 years
Federal agency mortgage-backed securities
Nuclear decommissioning trust fund disclosure
Fair Value	$ 100	$ 100
Unrealized Gains	3	1
Unrealized Losses	$ 0	$ 2
Weighted- average maturities (in years)	24 years	23 years
Commercial mortgage-backed securities
Nuclear decommissioning trust fund disclosure
Fair Value	$ 29	$ 22
Unrealized Gains	1	0
Unrealized Losses	$ 1	$ 1
Weighted- average maturities (in years)	24 years	22 years
Corporate debt securities
Nuclear decommissioning trust fund disclosure
Fair Value	$ 109	$ 96
Unrealized Gains	6	1
Unrealized Losses	$ 0	$ 2
Weighted- average maturities (in years)	11 years	11 years
Equity securities
Nuclear decommissioning trust fund disclosure
Fair Value	$ 466	$ 376
Unrealized Gains	324	231
Unrealized Losses	0	1
Foreign government fixed income securities
Nuclear decommissioning trust fund disclosure
Fair Value	5	4
Unrealized Gains	0	0
Unrealized Losses	$ 0	$ 0
Weighted- average maturities (in years)	10 years	9 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.

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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
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