Selected Balance Sheet Data Balance Sheet Related Disclosures, Property, Plant and Equipment (Details) - USD ($) $ in Thousands		Dec. 31, 2015	Dec. 31, 2014
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		$ 44,413,513	$ 41,535,142
Less accumulated depreciation		(13,591,259)	(13,168,418)
Property, plant and equipment, net		31,205,851	28,756,916
Electric plant
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		36,464,050	33,203,139
Natural gas plant
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		4,944,757	4,643,452
Common and other property
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		1,709,508	1,611,486
Plant to be retired
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	[1]	38,249	71,534
CWIP
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		1,256,949	2,005,531
Nuclear fuel
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		2,447,251	2,347,422
Less accumulated depreciation		$ (2,063,654)	$ (1,957,230)

[1] PSCo’s Cherokee Unit 3 was retired in August 2015. In 2017, PSCo expects to both early retire Valmont Unit 5 and convert Cherokee Unit 4 from a coal-fueled generating facility to natural gas, as approved by the CPUC. Amounts are presented net of accumulated depreciation.