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Operations and Significant Accounting Policies (Details) - USD ($) $ in Millions | Sep. 30, 2017 | Dec. 31, 2016
--- | --- | ---
Inventories – Net [Abstract] |  |  |
Fuel | [1] | $ 39.6 | $ 43.9
Materials and Supplies |  | 48.2 | 48.7
Raw Materials |  | 2.9 | 2.9
Work in Progress |  | 3.5 | 1.0
Finished Goods |  | 9.4 | 8.6
Reserve for Obsolescence |  | (1.0) | (0.9)
Total Inventories – Net |  | 102.6 | 104.2
Prepayments and Other Current Assets [Abstract] |  |  |
Deferred Fuel Adjustment Clause |  | 20.2 | 18.6
Restricted Cash |  | 6.5 | 2.2
Other |  | 17.5 | 19.5
Total Prepayments and Other Current Assets |  | 44.2 | 40.3
Other Non-Current Assets [Abstract] |  |  |
Contract Payment |  | 28.0 | 29.6
Finance Receivable |  | 11.0 | 11.5
Restricted Cash |  | 8.6 | 8.6
Other |  | 55.4 | 56.8
Total Other Non-Current Assets |  | 103.0 | 106.5
Other Current Liabilites [Abstract] |  |  |
PSAs |  | 24.8 | 24.6
Other |  | 59.9 | 49.1
Total Other Current Liabilities |  | 84.7 | 73.7
Other Non-Current Liabilities [Abstract] |  |  |
Asset Retirement Obligation |  | 157.4 | 136.6
PSAs |  | 95.3 | 113.8
Contingent Consideration | [2] | 5.6 | 25.0
Other |  | 42.8 | 47.3
Total Other Non-Current Liabilities |  | $ 301.1 | $ 322.7
[1] | Fuel consists primarily of coal inventory at Minnesota Power.
[2] | Contingent Consideration relates to the estimated fair value of the earnings-based payment resulting from the U.S. Water Services acquisition. (See Note 5. Fair Value.)

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