Selected Balance Sheet Data Balance Sheet Related Disclosures, Property, Plant and Equipment (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 14,751,325		$ 13,786,224
Less accumulated depreciation	(4,008,928)		(3,755,233)
Property, plant and equipment, net	10,742,397		10,030,991
Electric plant
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	10,177,056		9,782,163
Natural gas plant
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,757,605		2,583,394
Common and other property
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	762,916		761,712
Plant to be retired
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	101,279	[1]	152,730	[1]
Construction work in progress
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 952,469		$ 506,225

[1] As a result of the CPUC’s 2010 approval of PSCo’s CACJA compliance plan, subsequent CPCNs and the December 2013 approval of PSCo’s preferred plans for applicable generating resources, PSCo has received approval for early retirement of Cherokee Units 1, 2 and 3, Arapahoe Units 3 and 4 and Valmont Unit 5 between 2011 and 2017. In 2011, Cherokee Unit 2 was retired, in 2012, Cherokee Unit 1 was retired, and in 2013, Arapahoe Units 3 and 4 were retired. Amounts are presented net of accumulated depreciation.