Rate Matters (Details) (USD $)			9 Months Ended							1 Months Ended	3 Months Ended			1 Months Ended				12 Months Ended					1 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014 PSCo CPUC Proceeding - Colorado 2014 Electric Rate Case	Sep. 30, 2014 PSCo CPUC Proceeding - Colorado 2014 Electric Rate Case, Electric Rates 2015	Sep. 30, 2014 PSCo CPUC Proceeding - Colorado 2014 Electric Rate Case, Electric Rates 2016	Sep. 30, 2014 PSCo CPUC Proceeding - Colorado 2014 Electric Rate Case, Electric Rates 2017	Sep. 30, 2014 PSCo CPUC Proceeding - Manufacturer's Sales Tax Refund	Sep. 30, 2014 PSCo CPUC Proceeding - Annual Electric Earnings Test	Sep. 30, 2014 PSCo CPUC Proceeding - 2014 Electric Earnings Test	May 31, 2014 PSCo CPUC Proceeding - Renewable Energy Credit Sharing	Sep. 30, 2013 PSCo CPUC Proceeding - Renewable Energy Credit Sharing	Sep. 30, 2014 PSCo CPUC Proceeding - Renewable Energy Credit Sharing	Dec. 31, 2013 PSCo CPUC Proceeding - Renewable Energy Credit Sharing	Jun. 30, 2012 PSCo FERC Proceeding - Transmission Formula Rate Cases	Apr. 30, 2012 PSCo FERC Proceeding - Transmission Formula Rate Cases	Aug. 31, 2013 PSCo FERC Proceeding - Production Formula Rate ROE Complaint	Jul. 31, 2014 PSCo Colorado Public Utilities Commission (CPUC) CPUC Proceeding - 2013 Electric Earnings Test	Dec. 31, 2012 PSCo Colorado Public Utilities Commission (CPUC) CPUC Proceeding - Renewable Energy Credit Sharing	Dec. 31, 2012 PSCo Colorado Public Utilities Commission (CPUC) CPUC Proceeding - Renewable Energy Credit Sharing Shareholders	Dec. 31, 2011 PSCo Colorado Public Utilities Commission (CPUC) CPUC Proceeding - Renewable Energy Credit Sharing Shareholders	Dec. 31, 2012 PSCo Colorado Public Utilities Commission (CPUC) CPUC Proceeding - Renewable Energy Credit Sharing Customers	Dec. 31, 2011 PSCo Colorado Public Utilities Commission (CPUC) CPUC Proceeding - Renewable Energy Credit Sharing Customers	Oct. 31, 2014 Subsequent Event PSCo Federal Energy Regulatory Commission (FERC) FERC Proceeding - Transmission Formula Rate Cases	Oct. 31, 2014 Subsequent Event PSCo Federal Energy Regulatory Commission (FERC) FERC Proceeding - Production Formula Rate ROE Complaint	Aug. 31, 2013 Minimum PSCo FERC Proceeding - Production Formula Rate ROE Complaint	Aug. 31, 2013 Maximum PSCo FERC Proceeding - Production Formula Rate ROE Complaint
Rate Matters [Abstract]
Public Utilities, Requested Rate Increase (Decrease), Amount			$ 136,000,000												$ 2,000,000
Public Utilities, Requested Rate Increase (Decrease), Percentage			4.83%
Public Utilities, Portion of requested rate increase (decrease) attributable to CACJA recovery				100,900,000
Public Utilities, Requested increase (decrease) to rider revenue					34,200,000	29,900,000
Public Utilities, Requested Return on Equity, Percentage			10.35%											10.25%
Public Utilities, Requested Rate Base, Amount			6,390,000,000
Public Utilities, Requested Equity Capital Structure, Percentage			56.00%
Public Utilities, Rider costs to be recovered through base rates, Amount			19,900,000
Public Utilities, Maximum annual amount of property taxes not subject to deferral							76,700,000
Public Utilities, Reduction in current year property tax deferral							10,000,000
Public Utilities, Return on equity threshold triggering earnings sharing, Percentage								10.00%
Public Utilities, Refund Approved, Amount																	45,700,000
Regulatory Liability, Noncurrent	470,746,000	424,690,000							52,400,000
Public Utilities, Ultimate margin sharing associated with stand alone REC transactions, Percentage																				10.00%		90.00%
Public Utilities, Margin threshold determining percentage of margin sharing, Amount																		20,000,000
Public Utilities, Percentage of margin on hybrid REC approved for first 20 million of margins																			20.00%		80.00%
Public Utilities, Percentage of margin on hybrid REC approved for margins in excess of 20 million																			10.00%		90.00%
Public Utilities, Customers share of margins credited against RESA regulatory asset balance											6,100,000
Public Utilities, Cumulative credit against RESA regulatory asset balance												104,700,000	104,500,000
Public Utilities, Margin threshold proposed to be removed from sharing mechanism on hybrid REC trades, Amount										$ 20,000,000
Public Utilities, Return on equity requested by third parties, Percentage														9.15%		9.04%
Public Utilities, Approved Return on Equity, Percentage																							9.72%	9.72%
Public Utilities, Base return on equity charged to customers through production formula rates, Percentage																									10.10%	10.40%