Commitments and Contingencies, Fuel Contracts (Details) $ in Millions	12 Months Ended
Dec. 31, 2016 USD ($)
Coal
Fuel Contracts [Abstract]
2017	$ 707.6
2018	372.0
2019	102.7
2020	49.3
2021	50.4
Thereafter	295.1
Total	1,577.1
Nuclear Fuel
Fuel Contracts [Abstract]
2017	113.2
2018	60.8
2019	111.1
2020	37.7
2021	90.2
Thereafter	449.5
Total	862.5
Natural Gas Supply
Fuel Contracts [Abstract]
2017	395.6
2018	187.4
2019	181.4
2020	186.1
2021	193.3
Thereafter	172.0
Total	1,315.8
Natural Gas Storage and Transportation
Fuel Contracts [Abstract]
2017	252.0
2018	195.4
2019	155.1
2020	141.4
2021	132.9
Thereafter	1,108.8
Total	$ 1,985.6
Minimum
Unrecorded Unconditional Purchase Obligation [Line Items]
Fuel Contract Expiration Date	2017
Maximum
Unrecorded Unconditional Purchase Obligation [Line Items]
Fuel Contract Expiration Date	2060

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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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 440
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=73718637&loc=d3e25336-109308

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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

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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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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

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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

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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).

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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

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Date of fuel contract expiration

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