Selected Balance Sheet Data Balance Sheet Related Disclosures, Property, Plant and Equipment (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014		Dec. 31, 2013
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 15,252,031		$ 14,751,325
Less accumulated depreciation	(4,126,553)		(4,008,928)
Property, plant and equipment, net	11,125,478		10,742,397
Electric plant
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	10,356,644		10,177,056
Natural gas plant
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,866,667		2,757,605
Common and other property
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	751,236		762,916
Plant to be retired
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	85,808	[1]	101,279	[1]
Construction work in progress
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 1,191,676		$ 952,469

[1] As a result of the 2010 Colorado Public Utilities Commission (CPUC) approval of PSCo’s Clean Air Clean Jobs Act (CACJA) compliance plan and the December 2013 approval of PSCo’s preferred plans for applicable generating resources, PSCo has received approval for early retirement of Cherokee Unit 3 and Valmont Unit 5 between 2015 and 2017. Amounts are presented net of accumulated depreciation.