Summary of Significant Accounting Policies Materials, Supplies, and Inventories (Details) $ in Millions	Dec. 31, 2020 USD ($) $ / MMBTU	Dec. 31, 2019 USD ($) $ / MMBTU
Inventory
Natural gas in storage	$ 224.9	$ 227.7
Materials and supplies	218.1	234.2
Fossil fuel	85.6	87.9
Total	$ 528.6	$ 549.8
Percentage of LIFO inventory	22.00%	19.00%
PGL and NSG
Inventory
Excess of replacement or current costs over stated LIFO value	$ 31.5	$ 9.8
Natural gas price benchmark \| $ / MMBTU	2.31	1.95

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.

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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.

+ References

+ Details

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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.

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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.

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No definition available.

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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
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-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
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-Subparagraph (SX 210.5-02(6)(a)(5))
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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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No definition available.

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

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No definition available.

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