Commitments and Contingencies (Details) (USD $)	9 Months Ended
	Sep. 30, 2014
Natural Gas Supply Commitments [Member]
Recorded Unconditional Purchase Obligation Payment Schedule [Abstract]
2014	$ 232,000,000
2015	634,000,000
2016	557,000,000
2017	485,000,000
2018	434,000,000
After 2018	180,000,000
Gas Market Manipulation Cases [Member]
Recorded Unconditional Purchase Obligation Payment Schedule [Abstract]
Loss Contingency Pending Natural Gas Measurement Lawsuits Number	1
Loss Contingency, Amicus Briefs filed, number	4
Minnesota Service Territory [Member]
Recorded Unconditional Purchase Obligation Payment Schedule [Abstract]
Site Contingency Remaining Minnesota Sites	7
Site Contingency Sites Without Liability	2
Site Contingency Completed Remediation	2
LegalEnvironmentalAndOtherRegulatoryMattersLegalMattersGasMarketManipulationCasesAbstract
Accrual for Environmental Loss Contingencies	13,000,000
Annual amount included in rates to fund normal on-going remediation costs	285,000
Amount collected from insurance companies to be used for future environmental remediation	6,500,000
Minnesota Service Territory [Member] | Maximum [Member]
LegalEnvironmentalAndOtherRegulatoryMattersLegalMattersGasMarketManipulationCasesAbstract
Site Contingency, Loss Exposure Not Accrued, Low Estimate	41,000,000
Minimum years of remediation for the Minnesota sites (in years)	50
Minnesota Service Territory [Member] | Minimum [Member]
LegalEnvironmentalAndOtherRegulatoryMattersLegalMattersGasMarketManipulationCasesAbstract
Site Contingency, Loss Exposure Not Accrued, Low Estimate	6,000,000
Minimum years of remediation for the Minnesota sites (in years)	30
GenOn Demand Charges Transportation Contracts [Member]
LegalEnvironmentalAndOtherRegulatoryMattersLegalMattersGasMarketManipulationCasesAbstract
Guarantee of Affiliate Senior Notes	46,000,000
Enable Guaranteed Senior Notes [Member]
LegalEnvironmentalAndOtherRegulatoryMattersLegalMattersGasMarketManipulationCasesAbstract
Guarantee of Affiliate Senior Notes	$ 1,100,000,000