Property Plant and Equipment Property Plant and Equipment (Details) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property, plant and equipment		$ 19,911.0	$ 18,777.3
Property, plant and equipment, net		15,120.0	14,025.8
Electric plant
Property, Plant and Equipment [Line Items]
Property, plant and equipment		13,604.5	12,627.6
Natural gas plant
Property, Plant and Equipment [Line Items]
Property, plant and equipment		4,387.6	4,102.1
Common and other property
Property, Plant and Equipment [Line Items]
Property, plant and equipment		1,023.7	1,022.3
Plant to be retired
Property, Plant and Equipment [Line Items]
Property, plant and equipment	[1]	321.9	11.0
CWIP
Property, Plant and Equipment [Line Items]
Property, plant and equipment		573.3	1,014.3
Nuclear Fuel [Member]
Property, Plant and Equipment [Line Items]
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment		$ 4,791.0	$ 4,751.5

[1] (a) 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.