Income Taxes (Details) - USD ($)		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Income Tax Examination [Line Items]
Net Deferred Tax Liability associated with the Unrecognized Tax Benefit Amounts and Related NOLs and Tax Credit Carryforwards		$ (25,000,000)		$ (25,000,000)		$ (24,000,000)
Tax Audits [Abstract]
Unrecognized Tax Benefits, Income Tax Penalties Accrued		$ 0		$ 0		0
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		21.00%	21.00%	21.00%	21.00%
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent		5.00%	5.10%	5.00%	5.00%
Wind PTCs		(11.90%)	(5.40%)	(10.00%)	(5.80%)
Effective Income Tax Rate Reconciliation, Other Regulatory Items, Percent	[1]	(5.50%)	(2.40%)	(5.60%)	(1.80%)
Other tax credits and allowances (net)		(0.60%)	(1.10%)	(1.80%)	(1.20%)
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent		1.20%	(0.30%)	(0.50%)	(0.20%)
Effective Income Tax Rate Reconciliation, Percent		9.20%	16.90%	8.10%	17.00%
Unrecognized Tax Benefits [Abstract]
Unrecognized tax benefit — Permanent tax positions		$ 30,000,000		$ 30,000,000		28,000,000
Unrecognized tax benefit — Temporary tax positions		10,000,000		10,000,000		9,000,000
Total unrecognized tax benefit		40,000,000		40,000,000		37,000,000
NOL and tax credit carryforwards		(36,000,000)		(36,000,000)		$ (35,000,000)
Upper bound of decrease in unrecognized tax benefit that is reasonably possible		$ 28,000,000		28,000,000
Internal Revenue Service (IRS)
Tax Audits [Abstract]
Potential Tax Adjustments				0
Wisconsin
Tax Audits [Abstract]
Potential Tax Adjustments				$ 0

[1] Regulatory differences for income tax primarily relate to the flow back of excess deferred taxes to customers through the average rate assumption method and the impact of AFUDC - Equity. Quarterly variations primarily relates to the deferral of the flow back of excess deferred taxes in 2018, as a result of pending regulatory decisions. Treatment of most tax reform items was established prior to the first quarter of 2019, resulting in a reduction in deferred amounts. Income tax benefits associated with the flow back of excess deferred credits are offset by corresponding revenue reductions and additional prepaid pension asset amortization.