Income Taxes (Details) - USD ($)		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019		Jan. 01, 2019	Dec. 31, 2018	Jan. 01, 2018
Tax Audits [Abstract]
Tax Credit Carryforward, Amount							$ 7,000,000		$ 5,000,000
Environmental Remediation							6,000,000		6,000,000	[1]
Net Deferred Tax Liability associated with the Unrecognized Tax Benefit Amounts and Related NOLs and Tax Credit Carryforwards							(1,000,000)		(1,000,000)
Deferred Tax Assets, Tax Deferred Expense							36,000,000		5,000,000			$ 23,000,000
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		21.00%	21.00%	[1]	21.00%	[1]
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent		6.20%	6.20%	[1]	6.20%	[1]
Effective Income Tax Rate Reconciliation, Other Regulatory Items, Percent	[2]	(19.30%)	(5.20%)	[1]	(1.50%)	[1]
Amortization of excess nonplant deferred taxes		12.60%	0.00%	[1]
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent		(1.50%)	(1.80%)	[1]	(0.80%)	[1]
Effective Income Tax Rate Reconcilation, Change in unrecognized tax benefits, percent		(0.80%)	0.70%	[1]	0.40%	[1]
Reversal of prior regulatory differences		0.00%	3.60%	[1]	0.00%	[1]
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent		0.00%	(0.50%)	[1]	(0.70%)	[1]
Effective Income Tax Rate Reconciliation, Percent		(7.00%)	16.80%	[1]	24.60%	[1]
Deferred Tax Assets, Operating Loss Carryforwards, State and Local							2,000,000		2,000,000
Unrecognized Tax Benefits, Income Tax Penalties Expense		$ 0	$ 0		$ 0
Potential Federal Tax Adjustments		0
Income Tax Expense (Benefit)		(7,000,000)	16,000,000		32,000,000
Unrecognized Tax Benefits [Abstract]
Unrecognized Tax Benefits - Permanent tax positions							1,000,000		2,000,000
Unrecognized tax benefit — Temporary tax positions							1,000,000		1,000,000
Total unrecognized tax benefit		3,000,000	3,000,000		3,000,000		2,000,000	$ 3,000,000	3,000,000		$ 3,000,000	3,000,000	$ 2,000,000
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at Jan. 1		3,000,000	3,000,000
Unrecognized Tax Benefits Increases Resulting From Prior Period Tax Positions		1,000,000	0		1,000,000
Unrecognized Tax Benefits Decreases Resulting From Prior Period Tax Positions		(2,000,000)	0		0
Balance at Dec. 31		$ 2,000,000	$ 3,000,000		$ 3,000,000
Tax Benefits Associated With NOL And Tax Credit Carryforwards [Abstract]
NOL and tax credit carryforwards							(2,000,000)		(2,000,000)
Net Deferred Tax Liability associated with the Unrecognized Tax Benefit Amounts and Related NOLs and Tax Credit Carryforwards							(1,000,000)		(1,000,000)
Decrease in Unrecognized Tax Benefits is Reasonably Possible							1,000,000
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		21.00%	21.00%	[1]	21.00%	[1]
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent		6.20%	6.20%	[1]	6.20%	[1]
Effective Income Tax Rate Reconciliation, Other Regulatory Items, Percent	[2]	19.30%	5.20%	[1]	1.50%	[1]
Amortization of excess nonplant deferred taxes		12.60%	0.00%	[1]
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent		(1.50%)	(1.80%)	[1]	(0.80%)	[1]
Effective Income Tax Rate Reconciliation, Percent		(7.00%)	16.80%	[1]	24.60%	[1]
Components of Income Tax Expense (Benefit), Continuing Operations [Abstract]
Income Tax Expense (Benefit)		$ (7,000,000)	$ 16,000,000		$ 32,000,000
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]
Deferred tax expense (benefit) excluding selected items		9,000,000	17,000,000		24,000,000
Amortization and adjustments to deferred income taxes on income tax regulatory assets and liabilities		(45,000,000)	(12,000,000)		(1,000,000)
Deferred Income Tax Expense (Benefit)		$ (36,000,000)	$ 5,000,000		$ 23,000,000
Deferred Tax Assets, Gross [Abstract]
Deferred Tax Assets, Tax Deferred Expense							36,000,000		5,000,000			$ 23,000,000
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent		0.00%	(0.50%)	[1]	(0.70%)	[1]
Effective Income Tax Rate Reconcilation, Change in unrecognized tax benefits, percent		(0.80%)	0.70%	[1]	0.40%	[1]
Reversal of prior regulatory differences		0.00%	3.60%	[1]	0.00%	[1]
Net Deferred Tax Liablility [Member]
Tax Audits [Abstract]
Tax Credit Carryforward, Amount							8,000,000		5,000,000	[1]
Differences between book and tax basis of property		$ 324,000,000	$ 304,000,000	[1]
Regulatory Assets							32,000,000		50,000,000	[1]
Deferred tax liability - Pension expense							12,000,000		14,000,000	[1]
Deferred Tax Assets, Tax Deferred Expense, Other							9,000,000		7,000,000	[1]
Deferred Tax Liabilities, Tax Deferred Income							377,000,000		375,000,000	[1]
Regulatory Liabilities							41,000,000		47,000,000	[1]
other employee benefits							4,000,000		4,000,000	[1]
Deferred Tax Assets Rate Refund							4,000,000		9,000,000	[1]
Deferred ITCs		3,000,000	3,000,000	[1]
Deferred Tax Assets, Other							4,000,000		3,000,000	[1]
Deferred Tax Assets, Tax Deferred Expense							70,000,000		77,000,000	[1]
Deferred Tax Liabilities, Net							307,000,000		298,000,000	[1]
Deferred Tax Assets, Gross [Abstract]
Deferred Tax Assets Rate Refund							4,000,000		9,000,000	[1]
Deferred Tax Assets, Other							4,000,000		3,000,000	[1]
Deferred Tax Liabilities, Net							307,000,000		298,000,000	[1]
Regulatory Assets							32,000,000		50,000,000	[1]
Deferred tax liability - Pension expense							12,000,000		14,000,000	[1]
Deferred Tax Assets, Tax Deferred Expense, Other							9,000,000		7,000,000	[1]
Deferred Tax Liabilities, Tax Deferred Income							377,000,000		375,000,000	[1]
Differences between book and tax basis of property		324,000,000	304,000,000	[1]
Regulatory Liabilities							41,000,000		47,000,000	[1]
other employee benefits							4,000,000		4,000,000	[1]
Deferred ITCs		3,000,000	3,000,000	[1]
Deferred Tax Assets, Tax Deferred Expense							$ 70,000,000		$ 77,000,000	[1]
WISCONSIN
Tax Audits [Abstract]
Potential Tax Adjustments		0
income tax expense [Member]
Tax Audits [Abstract]
Deferred ITCs		1,000,000	1,000,000		$ 1,000,000
Current Federal Tax Expense (Benefit)		25,000,000	6,000,000		8,000,000
Current State and Local Tax Expense (Benefit)		6,000,000	5,000,000		2,000,000
Current Change In Unrecognized Tax Expense (Benefit)		(1,000,000)	1,000,000		0
Deferred Federal Income Tax Expense (Benefit)		(37,000,000)	3,000,000		16,000,000
Deferred State and Local Income Tax Expense (Benefit)		1,000,000	2,000,000		7,000,000
Income Tax Expense (Benefit)		(7,000,000)	16,000,000		32,000,000
Components of Income Tax Expense (Benefit), Continuing Operations [Abstract]
Current Federal Tax Expense (Benefit)		25,000,000	6,000,000		8,000,000
Current State and Local Tax Expense (Benefit)		6,000,000	5,000,000		2,000,000
Current Change In Unrecognized Tax Expense (Benefit)		(1,000,000)	1,000,000		0
Deferred Federal Income Tax Expense (Benefit)		(37,000,000)	3,000,000		16,000,000
Deferred State and Local Income Tax Expense (Benefit)		1,000,000	2,000,000		7,000,000
Income Tax Expense (Benefit)		(7,000,000)	16,000,000		32,000,000
Deferred Tax Assets, Gross [Abstract]
Deferred ITCs		$ 1,000,000	$ 1,000,000		$ 1,000,000

[1] Prior periods have been reclassified to conform to current year presentation.

[2] Regulatory differences for income tax primarily relate to the credit of excess deferred taxes to customers through the average rate assumption method. Income tax benefits associated with the credit of excess deferred credits are offset by corresponding revenue reductions.