Summary of Significant Accounting Policies - Inventory (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Summary of Significant Accounting Policies - Inventory [Abstract]
Energy Related Inventory, Other Fossil Fuel	$ 382	$ 257
Inventory, Raw Materials and Supplies, Gross	786	616
Replacement cost of inventory	$ 10
Replacement cost under stated LIFO value		2
Inventory [Line Items]
Replacement cost under stated LIFO value		$ 2

The amount replacement cost is below the stated LIFO (last in first out) inventory value at the balance sheet date.

No definition available.

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- Definition

Summary of Significant Accounting Policies - Inventory [Abstract]

+ References

No definition available.

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- Definition

Amount of fossil fuel included in inventory classified as other.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.6(a))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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- Definition

The excess of replacement or current cost over the stated LIFO (last in first out) inventory value when the LIFO inventory method is utilized.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.6(c))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

Gross amount of unprocessed materials to be used in manufacturing or production process and supplies that will be consumed.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.6(a)(4),(5))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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