Commitments and Contingencies Sherco (Details) - USD ($) $ in Millions	1 Months Ended
Jan. 31, 2021	Jan. 27, 2021
Public Utilities, General Disclosures [Line Items]
Amount MPUC previously disallowed related to Sherco outage		$ 22
NSP Minnesota
Public Utilities, General Disclosures [Line Items]
Customer refund of previously recovered purchased power costs	$ 17

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_PublicUtilitiesGeneralDisclosuresLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration