Commitments and Contingencies, Variable Interest Entities (Details) - MW	Dec. 31, 2021	Dec. 31, 2020
Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Purchased Power Agreements [Abstract]
Generating capacity (in MW)	1,347	1,347

Generating capacity under long-term purchased power agreements.

No definition available.

Name:	nspm_GeneratingCapacityUnderLongTermPurchasedPowerAgreements
Namespace Prefix:	nspm_
Data Type:	dtr-types:powerItemType
Balance Type:	na
Period Type:	instant