Summary of Significant Accounting Policies Materials, Supplies, and Inventories (Details) $ in Millions	Dec. 31, 2024 USD ($) $ / MMBTU	Dec. 31, 2023 USD ($) $ / MMBTU
Accounting Policies [Abstract]
Materials and supplies	$ 412.5	$ 320.0
Natural gas in storage	300.2	327.8
Fossil fuel	100.5	127.4
Total	$ 813.2	$ 775.2
LIFO Method Related Items [Abstract]
Percentage of LIFO inventory	18.00%	17.00%
Excess of replacement or current costs over stated LIFO value	$ 77.9	$ 12.2
Natural gas price benchmark \| $ / MMBTU	3.10	2.13

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Carrying amount as of the balance sheet date of merchandise, goods, commodities, or supplies relating to a source of usable power held for future sale or future use in manufacturing or production process.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
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Carrying amount as of the balance sheet date of natural gas in storage, which is a mixture of gases (liquefied or otherwise), used for fuel and manufacturing purposes, which is ready for sale.

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Amount of fossil fuel included in inventory classified as other.

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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://www.xbrl.org/2003/role/disclosureRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(6)(c))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

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Aggregated amount of unprocessed materials to be used in manufacturing or production process and supplies that will be consumed. This amount is net of valuation reserves and adjustments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 330
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 5.BB)
-Publisher FASB
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Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
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The percentage of LIFO (last in first out) inventory to total inventory as of the balance sheet date if other than 100 percent.

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Represents the Chicago city-gate natural gas price used in calculating replacement amounts.

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