Commitments and Contingencies, Legal Contingencies (Details) - PSCo [Member]	1 Months Ended		9 Months Ended
	Oct. 31, 2016 USD ($)	Dec. 31, 2015	Sep. 30, 2016 USD ($)
Line Extension Disputes
Legal Contingencies [Abstract]
Accrual for legal contingency			$ 0
Loss Contingency, Number of Plaintiffs			2
Minimum | Pacific Northwest FERC Refund Proceeding
Legal Contingencies [Abstract]
Amount Of Sales Claimed As Subject To Refund			$ 34,000,000
Minimum | Line Extension Disputes
Legal Contingencies [Abstract]
Loss Contingency, Number of Plaintiffs		50
Maximum | Pacific Northwest FERC Refund Proceeding
Legal Contingencies [Abstract]
Amount Of Sales Claimed As Subject To Refund			$ 50,000,000
Subsequent Event [Member] | Pacific Northwest FERC Refund Proceeding
Legal Contingencies [Abstract]
Litigation Settlement, Amount	$ 0