Property Plant and Equipment Joint Ownership of Generation, Transmission and Gas Facilities (Details) $ in Millions	Dec. 31, 2019 USD ($)
NSP Minnesota
Jointly Owned Utility Plant Interests [Line Items]
Plant in Service	$ 1,736
Accumulated Depreciation	627
CWIP	8
NSP Minnesota | Electric Generation | Sherco Unit 3
Jointly Owned Utility Plant Interests [Line Items]
Plant in Service	603
Accumulated Depreciation	426
CWIP	$ 4
Percent Owned	59.00%
NSP Minnesota | Electric Generation | Sherco Common Facilities
Jointly Owned Utility Plant Interests [Line Items]
Plant in Service	$ 145
Accumulated Depreciation	103
CWIP	$ 2
Percent Owned	80.00%
NSP Minnesota | Electric Generation | Sherco substation
Jointly Owned Utility Plant Interests [Line Items]
Plant in Service	$ 5
Accumulated Depreciation	3
CWIP	$ 0
Percent Owned	59.00%
NSP Minnesota | Electric Transmission | CapX2020
Jointly Owned Utility Plant Interests [Line Items]
Plant in Service	$ 972
Accumulated Depreciation	92
CWIP	$ 2
Percent Owned	51.00%
NSP Minnesota | Electric Transmission | Grand Meadow
Jointly Owned Utility Plant Interests [Line Items]
Plant in Service	$ 11
Accumulated Depreciation	3
CWIP	$ 0
Percent Owned	50.00%
NSP-Wisconsin
Jointly Owned Utility Plant Interests [Line Items]
Plant in Service	$ 356
Accumulated Depreciation	26
CWIP	0
NSP-Wisconsin | Electric Transmission | CapX2020
Jointly Owned Utility Plant Interests [Line Items]
Plant in Service	169
Accumulated Depreciation	19
CWIP	$ 0
Percent Owned	80.00%
NSP-Wisconsin | Electric Transmission | La Crosse, WI to Madison, WI
Jointly Owned Utility Plant Interests [Line Items]
Plant in Service	$ 187
Accumulated Depreciation	7
CWIP	$ 0
Percent Owned	37.00%
PSCo
Jointly Owned Utility Plant Interests [Line Items]
Plant in Service	$ 1,583
Accumulated Depreciation	459
CWIP	2
PSCo | Electric Generation | Hayden Unit 1
Jointly Owned Utility Plant Interests [Line Items]
Plant in Service	152
Accumulated Depreciation	81
CWIP	$ 0
Percent Owned	76.00%
PSCo | Electric Generation | Hayden Unit 2
Jointly Owned Utility Plant Interests [Line Items]
Plant in Service	$ 149
Accumulated Depreciation	71
CWIP	$ 0
Percent Owned	37.00%
PSCo | Electric Generation | Hayden Common Facilities
Jointly Owned Utility Plant Interests [Line Items]
Plant in Service	$ 41
Accumulated Depreciation	22
CWIP	$ 0
Percent Owned	53.00%
PSCo | Electric Generation | Craig Units 1 and 2
Jointly Owned Utility Plant Interests [Line Items]
Plant in Service	$ 81
Accumulated Depreciation	41
CWIP	$ 0
Percent Owned	10.00%
PSCo | Electric Generation | Craig Common Facilities
Jointly Owned Utility Plant Interests [Line Items]
Plant in Service	$ 39
Accumulated Depreciation	22
CWIP	$ 0
Percent Owned	7.00%
PSCo | Electric Generation | Comanche Unit 3
Jointly Owned Utility Plant Interests [Line Items]
Plant in Service	$ 887
Accumulated Depreciation	149
CWIP	$ 1
Percent Owned	67.00%
PSCo | Electric Generation | Comanche Common Facilities
Jointly Owned Utility Plant Interests [Line Items]
Plant in Service	$ 29
Accumulated Depreciation	3
CWIP	$ 0
Percent Owned	82.00%
PSCo | Electric Transmission | Transmission and other facilities
Jointly Owned Utility Plant Interests [Line Items]
Plant in Service	$ 174
Accumulated Depreciation	62
CWIP	1
PSCo | Gas Transportation | Rifle, CO to Avon, CO
Jointly Owned Utility Plant Interests [Line Items]
Plant in Service	22
Accumulated Depreciation	7
CWIP	$ 0
Percent Owned	60.00%
PSCo | Gas Transportation | Gas Transportation Compressor
Jointly Owned Utility Plant Interests [Line Items]
Plant in Service	$ 9
Accumulated Depreciation	1
CWIP	$ 0
Percent Owned	50.00%