Selected Balance Sheet Data Balance Sheet Related Disclosures, Property, Plant and Equipment (Details) - USD ($) $ in Millions		Sep. 30, 2019	Dec. 31, 2018
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		$ 20,871.5	$ 19,911.0
Less accumulated depreciation		(5,085.1)	(4,791.0)
Property, plant and equipment, net		15,786.4	15,120.0
Electric plant
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		14,070.5	13,604.5
Natural gas plant
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		4,526.5	4,387.6
Common and other property
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		1,070.2	1,023.7
Plant to be retired
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	[1]	275.5	321.9
Construction work in progress
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		$ 928.8	$ 573.3

[1] In 2018, the CPUC approved early retirement of PSCo’s Comanche Units 1 and 2 in approximately 2022 and 2025, respectively. PSCo also expects Craig Unit 1 to be retired early in 2025. Amounts are presented net of accumulated depreciation.