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Summary of Significant Accounting Policies AFUDC (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Allowance for Funds Used During Construction |  |  |
AFUDC - Debt | $ 4.9 | $ 10.9 | $ 8.6
AFUDC - Equity | $ 11.4 | $ 25.1 | $ 20.1
WE |  |  |
Allowance for Funds Used During Construction |  |  |
Percentage of retail jurisdictional construction work in progress expenditure subject to public utilities allowance for funds used during construction calculation | 50.00% |  |
WPS |  |  |
Allowance for Funds Used During Construction |  |  |
Percentage of retail jurisdictional construction work in progress expenditure subject to public utilities allowance for funds used during construction calculation | 50.00% |  |
WBS |  |  |
Allowance for Funds Used During Construction |  |  |
Percentage of retail jurisdictional construction work in progress expenditure subject to public utilities allowance for funds used during construction calculation | 50.00% |  |
WG |  |  |
Allowance for Funds Used During Construction |  |  |
Percentage of retail jurisdictional construction work in progress expenditure subject to public utilities allowance for funds used during construction calculation | 50.00% |  |
Retail operations | WE |  |  |
Allowance for Funds Used During Construction |  |  |
Interest rate on accrued AFUDC | 8.45% |  |
Retail operations | WPS |  |  |
Allowance for Funds Used During Construction |  |  |
Interest rate on accrued AFUDC | 7.72% |  |
Retail operations | WBS |  |  |
Allowance for Funds Used During Construction |  |  |
Interest rate on accrued AFUDC | 7.72% |  |
Retail operations | WG |  |  |
Allowance for Funds Used During Construction |  |  |
Interest rate on accrued AFUDC | 8.33% |  |
Wholesale operations | WE |  |  |
Allowance for Funds Used During Construction |  |  |
Interest rate on accrued AFUDC | 5.94% |  |
Wholesale operations | WPS |  |  |
Allowance for Funds Used During Construction |  |  |
Interest rate on accrued AFUDC | 1.01% |  |

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- Definition The component of the allowance for funds used during construction during the period based on an assumed rate of return on equity funds used in financing the construction of regulated assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 835 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6501569&loc=d3e55921-110430 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 835 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6501662&loc=d3e56162-110433 + Details
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- Definition Amount capitalized of allowance for funds used during construction. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 835 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6501569&loc=d3e55921-110430 + Details
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- Definition Effective rate, including composite rate, of cost of financing additions to qualifying regulated assets, commonly called allowance for funds used during construction. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 835 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6501662&loc=d3e56162-110433 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 835 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6501569&loc=d3e55921-110430 + Details
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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 Represents the percentage of retail jurisdictional construction work in progress expenditures subject to the AFUDC calculation. + References No definition available. + Details
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