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Risk Management Activities (Schedule of Derivative Instruments in Statement of Financial Position, Fair Value) (Details) - USD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Derivatives, Fair Value [Line Items] |  |
Derivative Asset | $ 13.2 | $ 4.4
Derivative Liability | 222.8 | 146.6
Risk Management Assets Current |  |
Derivatives, Fair Value [Line Items] |  |
Derivative Asset | 10.4 | 0.6
Risk Management Assets Noncurrent |  |
Derivatives, Fair Value [Line Items] |  |
Derivative Asset | 2.8 | 3.8
Risk Management Liabilities Current |  |
Derivatives, Fair Value [Line Items] |  |
Derivative Liability | 78.2 | 12.6
Risk Management Liabilities Noncurrent |  |
Derivatives, Fair Value [Line Items] |  |
Derivative Liability | 144.6 | 134.0
Interest rate risk programs | Risk Management Assets Current |  |
Derivatives, Fair Value [Line Items] |  |
Derivative Asset | 0.0 | 0.0
Interest rate risk programs | Risk Management Assets Noncurrent |  |
Derivatives, Fair Value [Line Items] |  |
Derivative Asset | 0.0 | 0.0
Interest rate risk programs | Risk Management Liabilities Current |  |
Derivatives, Fair Value [Line Items] |  |
Derivative Liability | 70.9 | 0.0
Interest rate risk programs | Risk Management Liabilities Noncurrent |  |
Derivatives, Fair Value [Line Items] |  |
Derivative Liability | 99.5 | 76.2
Commodity price risk programs | Risk Management Assets Current |  |
Derivatives, Fair Value [Line Items] |  |
Derivative Asset | 10.4 | 0.6
Commodity price risk programs | Risk Management Assets Noncurrent |  |
Derivatives, Fair Value [Line Items] |  |
Derivative Asset | 2.8 | 3.8
Commodity price risk programs | Risk Management Liabilities Current |  |
Derivatives, Fair Value [Line Items] |  |
Derivative Liability | 7.3 | 12.6
Commodity price risk programs | Risk Management Liabilities Noncurrent |  |
Derivatives, Fair Value [Line Items] |  |
Derivative Liability | $ 45.1 | $ 57.8

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- Definition Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226008-175313 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=121572278&loc=d3e13433-108611 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312 + Details
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