Selected Balance Sheet Data Balance Sheet Related Disclosures, Property, Plant and Equipment (Details) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		$ 46,832,219	$ 44,413,513
Less accumulated depreciation		(14,381,603)	(13,591,259)
Property, plant and equipment, net		32,841,750	31,205,851
Electric plant
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		38,220,765	36,464,050
Natural gas plant
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		5,317,717	4,944,757
Common and other property
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		1,888,518	1,709,508
Plant to be retired
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	[1]	31,839	38,249
CWIP
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		1,373,380	1,256,949
Nuclear fuel
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		2,571,770	2,447,251
Less accumulated depreciation		$ (2,180,636)	$ (2,063,654)

[1] In 2017, PSCo expects to early retire Valmont Unit 5 and convert Cherokee Unit 4 from a coal-fueled generating facility to natural gas. PSCo also expects Craig Unit 1 to be early retired in approximately 2025. Amounts are presented net of accumulated depreciation.