Fair Value of Financial Instruments - Assets and Liabilities Measured and Recorded at Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in securities (classified within other current and non-current assets)	$ 24	$ 25
Other trust fund investments:
U.S. government and federal agency obligations	1	1
Measured using net asset value practical expedient:
Total assets	3,766	1,745
Derivative liabilities:
Commodity contracts	2,440	884
Commodity contracts
Derivative assets:
Commodity contracts	2,824	821
Derivative liabilities:
Commodity contracts	2,438	884
Foreign exchange contract
Derivative liabilities:
Commodity contracts	2
Cash and cash equivalents
Nuclear trust fund investments:
Nuclear trust fund investments	20	23
U.S. government and federal agency obligations
Nuclear trust fund investments:
Nuclear trust fund investments	73	70
Federal agency mortgage-backed securities
Nuclear trust fund investments:
Nuclear trust fund investments	78	89
Commercial mortgage-backed securities
Nuclear trust fund investments:
Nuclear trust fund investments	40	36
Corporate debt securities
Nuclear trust fund investments:
Nuclear trust fund investments	136	144
Equity securities
Nuclear trust fund investments:
Nuclear trust fund investments	466	434
Measured using net asset value practical expedient:
Equity securities	8	8
Foreign government fixed income securities
Nuclear trust fund investments:
Nuclear trust fund investments	7	7
Equity securities — nuclear trust fund investments
Measured using net asset value practical expedient:
Equity securities	89	87
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in securities (classified within other current and non-current assets)	10	10
Other trust fund investments:
U.S. government and federal agency obligations	1	1
Measured using net asset value practical expedient:
Total assets	765	597
Derivative liabilities:
Commodity contracts	205	86
Level 1 \| Commodity contracts
Derivative assets:
Commodity contracts	195	59
Derivative liabilities:
Commodity contracts	205	86
Level 1 \| Foreign exchange contract
Derivative liabilities:
Commodity contracts	0
Level 1 \| Cash and cash equivalents
Nuclear trust fund investments:
Nuclear trust fund investments	20	23
Level 1 \| U.S. government and federal agency obligations
Nuclear trust fund investments:
Nuclear trust fund investments	72	69
Level 1 \| Federal agency mortgage-backed securities
Nuclear trust fund investments:
Nuclear trust fund investments	0	0
Level 1 \| Commercial mortgage-backed securities
Nuclear trust fund investments:
Nuclear trust fund investments	0	0
Level 1 \| Corporate debt securities
Nuclear trust fund investments:
Nuclear trust fund investments	0	0
Level 1 \| Equity securities
Nuclear trust fund investments:
Nuclear trust fund investments	466	434
Level 1 \| Foreign government fixed income securities
Nuclear trust fund investments:
Nuclear trust fund investments	1	1
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in securities (classified within other current and non-current assets)	14	15
Other trust fund investments:
U.S. government and federal agency obligations	0	0
Measured using net asset value practical expedient:
Total assets	2,640	914
Derivative liabilities:
Commodity contracts	2,130	643
Level 2 \| Commodity contracts
Derivative assets:
Commodity contracts	2,365	623
Derivative liabilities:
Commodity contracts	2,128	643
Level 2 \| Foreign exchange contract
Derivative liabilities:
Commodity contracts	2
Level 2 \| Cash and cash equivalents
Nuclear trust fund investments:
Nuclear trust fund investments	0	0
Level 2 \| U.S. government and federal agency obligations
Nuclear trust fund investments:
Nuclear trust fund investments	1	1
Level 2 \| Federal agency mortgage-backed securities
Nuclear trust fund investments:
Nuclear trust fund investments	78	89
Level 2 \| Commercial mortgage-backed securities
Nuclear trust fund investments:
Nuclear trust fund investments	40	36
Level 2 \| Corporate debt securities
Nuclear trust fund investments:
Nuclear trust fund investments	136	144
Level 2 \| Equity securities
Nuclear trust fund investments:
Nuclear trust fund investments	0	0
Level 2 \| Foreign government fixed income securities
Nuclear trust fund investments:
Nuclear trust fund investments	6	6
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in securities (classified within other current and non-current assets)	0	0
Other trust fund investments:
U.S. government and federal agency obligations	0	0
Measured using net asset value practical expedient:
Total assets	264	139
Derivative liabilities:
Commodity contracts	105	155
Level 3 \| Commodity contracts
Derivative assets:
Commodity contracts	264	139
Derivative liabilities:
Commodity contracts	105	155
Level 3 \| Foreign exchange contract
Derivative liabilities:
Commodity contracts	0
Level 3 \| Cash and cash equivalents
Nuclear trust fund investments:
Nuclear trust fund investments	0	0
Level 3 \| U.S. government and federal agency obligations
Nuclear trust fund investments:
Nuclear trust fund investments	0	0
Level 3 \| Federal agency mortgage-backed securities
Nuclear trust fund investments:
Nuclear trust fund investments	0	0
Level 3 \| Commercial mortgage-backed securities
Nuclear trust fund investments:
Nuclear trust fund investments	0	0
Level 3 \| Corporate debt securities
Nuclear trust fund investments:
Nuclear trust fund investments	0	0
Level 3 \| Equity securities
Nuclear trust fund investments:
Nuclear trust fund investments	0	0
Level 3 \| Foreign government fixed income securities
Nuclear trust fund investments:
Nuclear trust fund investments	$ 0	$ 0

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Decommission fund to pay for the costs of decontaminating and decommissioning of facilities through collection of revenues derived from utility assessments and government appropriations. Decommission fund investment for the process whereby a power station, at the end of its economic life, is taken permanently out of service and its site made available for other purposes. In the case of a nuclear station this comprises three different states of clearance. Immediately after the final closure, radioactive material such as nuclear fuel and operational waste is removed and the buildings surrounding the reactor shield are dismantled and finally the reactor itself is dismantled.

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