Investment in ATC - FERC Complaint (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014
Loss Contingencies [Line Items]
Equity Method Investment, Proposed Return on Common Equity	9.15%
Equity Method Investment, Approved Return on Common Equity	12.20%
Equity Method Investment, Ownership Percentage	8.00%
Sensitivity Analysis [Member]
Sensitivity Analysis [Line Items]
Basis Point Reduction on Approved Rate of Return on Common Equity	50
Effect on Future Earnings, Amount	$ 0.5
ATC [Member]
Loss Contingencies [Line Items]
Loss Contingency, Estimate of Possible Loss	18
Rainy River Energy [Member]
Loss Contingencies [Line Items]
Loss Contingency, Estimate of Possible Loss	$ 1