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Regulatory Matters - Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2015 | Dec. 31, 2014
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets and Liabilities Currently Earning a Return |  | No regulatory assets or liabilities are currently earning a return. |
Current Regulatory Asset |  | $ 10.6 | $ 16.3
Non-Current Regulatory Asset |  | 372.0 | 357.3
Total Regulatory Assets |  | 382.6 | 373.6
Non-Current Regulatory Liability |  | 105.0 | 94.2
Wholesale and Retail Contra AFUDC [Member] |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Non-Current Regulatory Liability | [1] | 58.0 | 42.9
Plant Removal Obligations [Member] |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Non-Current Regulatory Liability |  | 22.1 | 22.8
Income Taxes [Member] |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Non-Current Regulatory Liability | [2] | 6.1 | 13.4
Defined Benefit Pension and Other Postretirement Benefit Plans [Member] |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Non-Current Regulatory Liability | [3] | 0.9 | 3.5
Other [Member] |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Non-Current Regulatory Liability |  | 17.9 | 11.6
Deferred Fuel Adjustment Clause [Member] |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Current Regulatory Asset | [4] | 10.6 | 16.3
Defined Benefit Pension and Other Postretirement Benefit Plans [Member] |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Non-Current Regulatory Asset | [3] | 219.3 | 223.9
Income Taxes [Member] |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Non-Current Regulatory Asset | [2] | 64.2 | 46.6
Cost Recovery Riders [Member] |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Non-Current Regulatory Asset | [5] | 58.0 | 59.7
Asset Retirement Obligation [Member] |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Non-Current Regulatory Asset | [6] | 21.6 | 17.8
PPACA Income Tax Deferral [Member] |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Non-Current Regulatory Asset |  | 5.0 | 5.0
Other [Member] |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Non-Current Regulatory Asset |  | $ 3.9 | $ 4.3
[1] | Wholesale and Retail Contra AFUDC represents amortization to offset AFUDC Equity and Debt recorded during the construction period of our cost recovery rider projects prior to placing the projects in service. The regulatory liability will decrease over the remaining depreciable life of the related asset.
[2] | These costs represent the difference between deferred income taxes recognized for financial reporting purposes and amounts previously billed to our customers. This balance will decrease over the remaining life of the related temporary differences and flow through current income taxes.
[3] | Defined benefit pension and other postretirement items included in our Regulated Operations, which are otherwise required to be recognized in accumulated other comprehensive income as actuarial gains and losses as well as prior service costs and credits, are recognized as regulatory assets or regulatory liabilities on the Consolidated Balance Sheet. The asset or liability will decrease as the deferred items are amortized and recognized as components of net periodic benefit cost. (See Note 17. Pension and Other Postretirement Benefit Plans.)
[4] | Current regulatory assets are included in Prepayments and Other on the Consolidated Balance Sheet.
[5] | The cost recovery rider regulatory assets are revenues not yet collected from our customers primarily due to capital expenditures related to the Bison Wind Energy Center, investment in CapX2020 projects, and the Boswell Unit 4 environmental upgrade and are recognized in accordance with the accounting standards for alternative revenue programs.
[6] | Asset retirement obligations will accrete and be amortized over the lives of the related property with asset retirement obligations.

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- Definition The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382 + Details
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- Definition Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382 + Details
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