Commitments and Contingencies, Fuel Contracts (Details) $ in Millions	12 Months Ended
Dec. 31, 2015 USD ($)
Coal
Fuel Contracts [Abstract]
2016	$ 824.4
2017	483.0
2018	227.8
2019	42.7
2020	44.4
Thereafter	334.9
Total	1,957.2
Nuclear Fuel
Fuel Contracts [Abstract]
2016	112.2
2017	112.3
2018	62.7
2019	124.1
2020	46.9
Thereafter	599.2
Total	1,057.4
Natural Gas Supply
Fuel Contracts [Abstract]
2016	285.4
2017	132.2
2018	181.0
2019	187.6
2020	203.4
Thereafter	409.5
Total	1,399.1
Natural Gas Storage and Transportation
Fuel Contracts [Abstract]
2016	282.0
2017	254.9
2018	154.5
2019	113.8
2020	101.6
Thereafter	1,044.2
Total	$ 1,951.0
Minimum
Unrecorded Unconditional Purchase Obligation [Line Items]
Fuel Contract Expiration Date	2016
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=6394976&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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