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Property, Plant and Equipment (Narrative) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Property, Plant and Equipment [Line Items] |  |  |
Plant and Equipment Associated with Schahfer Generating Station Retirement |  | $ 903.8 |
Depreciation | $ 672.1 | 655.6 | $ 612.2
Regulatory Deferral - Joint Venture | 5.3 |  |
Capitalized Computer Software, Amortization | 49.4 | 56.7 | 55.5
Capitalized Computer Software, Gross | 181.8 | 136.4 |
Capitalized Cloud Computing, Amortization | 10.0 | 3.4 | $ 1.6
Capitalized Cloud Computing, Gross | 42.4 | $ 12.7 |
Units 14 and 15 |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Plant and Equipment Associated with Schahfer Generating Station Retirement | 600.0 |  |
Units Not Retired |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Plant and Equipment Associated with Schahfer Generating Station Retirement | $ 201.5 |  |

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- Definition Amount of expense for amortization of capitalized computer software costs. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 985 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=6501960&loc=d3e128462-111756 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 985 -SubTopic 20 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6501960&loc=d3e128487-111756 + Details
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- Definition Amount before accumulated amortization of capitalized costs for computer software, including but not limited to, acquired and internally developed computer software. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 985 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6501960&loc=d3e128462-111756 + Details
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- Definition The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3602-108585 + Details
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