Commitments and Contingencies, Fuel Contracts (Details) $ in Millions	12 Months Ended
Dec. 31, 2018 USD ($)
Fuel Contracts [Abstract]
Minimum annual tolerance band percentage for future rate recovery or refund of fuel costs	2.00%
Coal
Fuel Contracts [Abstract]
2019	$ 6.1
2020	2.3
2021	0.6
2022	0.7
2023	0.7
Thereafter	0.0
Total	10.4
Natural Gas Supply
Fuel Contracts [Abstract]
2019	9.9
2020	0.3
2021	0.4
2022	0.2
2023	0.0
Thereafter	0.0
Total	10.8
Natural Gas Storage and Transportation
Fuel Contracts [Abstract]
2019	13.4
2020	11.8
2021	11.3
2022	9.7
2023	7.9
Thereafter	24.3
Total	$ 78.4
Minimum
Unrecorded Unconditional Purchase Obligation [Line Items]
Fuel Contract Expiration Date	2019
Maximum
Unrecorded Unconditional Purchase Obligation [Line Items]
Fuel Contract Expiration Date	2029

Date of fuel contract expiration

No definition available.

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- Definition

The minimum annual tolerance band percentage for future rate recovery or refund related to the deferral of the under-collection or over-collection of fuel costs.

+ References

No definition available.

+ Details

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- References

No definition available.

+ Details

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- Definition

Amount of the fixed and determinable portion of the unrecorded unconditional purchase obligation maturing in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 440
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=77896938&loc=d3e25336-109308

+ Details

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- Definition

Amount of the fixed and determinable portion of the unrecorded unconditional purchase obligation maturing in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

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- Definition

Amount of the fixed and determinable portion of the unrecorded unconditional purchase obligation maturing in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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- Definition

Amount of the fixed and determinable portion of the unrecorded unconditional purchase obligation maturing in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

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- Definition

Amount of the fixed and determinable portion of the unrecorded unconditional purchase obligation maturing in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

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- Definition

Amount of the unrecorded obligation to transfer funds in the future for fixed or minimum amounts or quantities of goods or services at fixed or minimum prices (for example, as in take-or-pay contracts or throughput contracts).

+ References

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- Definition

Amount of the fixed and determinable portion of the unrecorded unconditional purchase obligation maturing after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ 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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