MGP, Landfill and Disposal Sites (Details) $ in Millions	6 Months Ended
	Jun. 30, 2020 USD ($) Period	Dec. 31, 2019 USD ($)
Other MGP, Landfill, or Disposal Sites [Domain]
Manufactured Gas Plant (MGP) Site [Abstract]
Number of identified MGP, landfill, or disposal sites under current investigation and/or remediation	12
NSP-Wisconsin | Ashland MGP Site
Manufactured Gas Plant (MGP) Site [Abstract]
Current Cost Estimate for Site Remediation	$ 199
Accrual for Environmental Loss Contingencies, Gross	$ 21	$ 23
Carrying cost percentage to be applied to unamortized regulatory asset	3.00%
Maximum [Member] | PSCo [Member] | Denver MGP Site [Member]
Site Contingency [Line Items]
Time period of future environmental, investigation, remediation and mitigation measures | Period	15
Manufactured Gas Plant (MGP) Site [Abstract]
Future environmental investigation, remediation or mitigation	$ 9