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Commitments and Contingencies NSP-Minnesota - MEC Transactions (Details) $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2020 USD ($) MW	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Public Utilities, General Disclosures [Line Items]
Other Liabilities, Current		$ 396	$ 468
Liabilities, Current		5,473	$ 4,568
MEC Holdings LLC [Member]
Public Utilities, General Disclosures [Line Items]
Disposal Group, Including Discontinued Operation, Liabilities		11
Assets Held-for-sale, Long Lived, Fair Value Disclosure		668
Other Assets, Current		24
Other Liabilities, Current		2
Other Assets		644
Contract with Customer, Liability		9
MEC Holdings LLC [Member] \| Unregulated Operation [Member]
Public Utilities, General Disclosures [Line Items]
Facility Output \| MW	760
PP&E Additions	$ 650
MEC Holdings LLC [Member] \| Unregulated Operation [Member] \| Southwest Generation [Domain]
Public Utilities, General Disclosures [Line Items]
PP&E Sale		$ 680