Balance Sheet Related Disclosures, Property, Plant and Equipment (Details) - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		$ 49,580	$ 48,927
Less accumulated depreciation		(15,276)	(15,000)
Property, plant and equipment, net		34,679	34,329
Electric plant
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		39,348	39,016
Natural gas plant
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		5,855	5,800
Common and other property
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		2,027	2,013
Plant to be retired
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	[1]	11	11
Construction work in progress
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		2,339	2,087
Nuclear fuel
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		2,701	2,697
Less accumulated depreciation		$ (2,326)	$ (2,295)

[1] In the third quarter of 2017, PSCo early retired Valmont Unit 5 and converted 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.