Balance Sheet Related Disclosures, Property, Plant and Equipment (Details) - USD ($) $ in Thousands		Mar. 31, 2017	Dec. 31, 2016
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		$ 47,294,166	$ 46,832,219
Less accumulated depreciation		(14,576,320)	(14,381,603)
Property, plant and equipment, net		33,158,384	32,841,750
Electric plant
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		38,412,137	38,220,765
Natural gas plant
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		5,365,655	5,317,717
Common and other property
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		1,897,263	1,888,518
Plant to be retired
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	[1]	22,202	31,839
Construction work in progress
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		1,596,909	1,373,380
Nuclear fuel
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		2,652,026	2,571,770
Less accumulated depreciation		$ (2,211,488)	$ (2,180,636)

[1] In the fourth quarter of 2017, PSCo expects to both 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.