Commitments and Contingencies, Legal Contingencies (Details)	1 Months Ended		12 Months Ended
	Oct. 31, 2016 USD ($)	Dec. 31, 2015	Dec. 31, 2016 USD ($)
Pacific Northwest FERC Refund Proceeding
Legal Contingencies [Abstract]
Accrual For Legal Contingency			$ 0
PSCo | Pacific Northwest FERC Refund Proceeding
Legal Contingencies [Abstract]
Litigation Settlement, Amount	$ 15,000
PSCo | Line Extension Disputes
Legal Contingencies [Abstract]
Accrual For Legal Contingency			$ 0
Loss Contingency, Number of Plaintiffs			2
Maximum | PSCo | Pacific Northwest FERC Refund Proceeding
Legal Contingencies [Abstract]
Amount of Sales Claimed as Subject to Refund			$ 50,000,000
Minimum | PSCo | Pacific Northwest FERC Refund Proceeding
Legal Contingencies [Abstract]
Amount of Sales Claimed as Subject to Refund			$ 34,000,000
Minimum | PSCo | Line Extension Disputes
Legal Contingencies [Abstract]
Loss Contingency, Number of Plaintiffs		50