Fair Value of Financial Assets and Liabilities - Recurring Fair Value Measurements (Details) MMBTU in Millions, $ in Millions		Mar. 31, 2022 USD ($) MMBTU	Dec. 31, 2021 USD ($) MMBTU
Derivatives, Fair Value [Line Items]
Prepayments and other		$ 9	$ 7
Natural Gas Commodity [Member]
Derivatives, Fair Value [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU		0	0
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Natural Gas Commodity
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross			$ 1
Netting	[1]		0
Derivative Asset, Net		$ 0	1	[2],[3]
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Natural Gas Commodity | Level 1
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross			0
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Natural Gas Commodity | Level 2
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross			1
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Natural Gas Commodity | Level 3
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross			$ 0

[1] NSP-Wisconsin nets derivative instruments and related collateral on its consolidated balance sheets when supported by a legally enforceable master netting agreement, and all derivative instruments and related collateral amounts were subject to master netting agreements at Dec. 31, 2021. The counterparty netting amounts presented exclude settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.

[2] Included in other current liabilities at Dec. 31, 2021 on the consolidated balance sheets.

[3] Included in prepayments and other current assets at Dec. 31, 2021 on the consolidated balance sheets.