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	$ 39,627,910		$ 38,386,353
Less accumulated depreciation	(12,854,913)		(12,608,305)
Property, plant and equipment, net	27,070,377		26,122,159
Electric plant
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	31,360,194		30,341,310
Natural gas plant
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	4,211,851		4,086,651
Common and other property
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,467,336		1,485,547
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	2,502,721		2,371,566
Nuclear fuel
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,200,534		2,186,799
Less accumulated depreciation	$ (1,903,154)		$ (1,842,688)

[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.