REGULATORY ENVIRONMENT - WI 2020 AND 2021 RATES - AUGUST SETTLEMENTS (Details) - Public Service Commission of Wisconsin (PSCW) $ in Millions	1 Months Ended
	Aug. 31, 2019 USD ($) utility	Mar. 31, 2019 USD ($)
August 2019 Settlement Agreement | Electric rates | Tax Cuts and Jobs Act of 2017
Public Utilities, General Disclosures [Line Items]
Amortization period	2 years
August 2019 Settlement Agreement | Natural gas rates | Tax Cuts and Jobs Act of 2017
Public Utilities, General Disclosures [Line Items]
Amortization period	4 years
Number of gas utilities amortizing unprotected deferred tax expense over 4 years | utility	3
August 2019 Settlement Agreement | WE | 2020 and 2021 rates
Public Utilities, General Disclosures [Line Items]
Requested return on equity (as a percent)	10.00%
Requested common equity component average (as a percent)	52.50%
August 2019 Settlement Agreement | WE | Electric rates
Public Utilities, General Disclosures [Line Items]
Pleasant Prairie power plant's book value to be securitized	$ 100
August 2019 Settlement Agreement | WE | Electric rates | 2020 rates
Public Utilities, General Disclosures [Line Items]
Requested rate increase	$ 37
Requested rate increase (as a percent)	1.30%
August 2019 Settlement Agreement | WE | Electric rates | 2020 rates | Tax Cuts and Jobs Act of 2017
Public Utilities, General Disclosures [Line Items]
Amortization of regulatory liabilities	$ 65
August 2019 Settlement Agreement | WE | Electric rates | 2021 rates | Tax Cuts and Jobs Act of 2017
Public Utilities, General Disclosures [Line Items]
Amortization of regulatory liabilities	65
August 2019 Settlement Agreement | WE | Natural gas rates | 2020 rates
Public Utilities, General Disclosures [Line Items]
Requested rate increase	$ 10
Requested rate increase (as a percent)	2.80%
August 2019 Settlement Agreement | WE | Natural gas rates | 2020 rates | Tax Cuts and Jobs Act of 2017
Public Utilities, General Disclosures [Line Items]
Amortization of regulatory liabilities	$ (5)
August 2019 Settlement Agreement | WE | Natural gas rates | 2021 rates | Tax Cuts and Jobs Act of 2017
Public Utilities, General Disclosures [Line Items]
Amortization of regulatory liabilities	(5)
August 2019 Settlement Agreement | WE | Steam rates | 2020 rates
Public Utilities, General Disclosures [Line Items]
Requested rate increase	$ 2
Requested rate increase (as a percent)	10.00%
August 2019 Settlement Agreement | WG | 2020 and 2021 rates
Public Utilities, General Disclosures [Line Items]
Requested return on equity (as a percent)	10.20%
Requested common equity component average (as a percent)	52.50%
August 2019 Settlement Agreement | WG | Natural gas rates | 2020 rates
Public Utilities, General Disclosures [Line Items]
Requested rate increase	$ (1)
Requested rate increase (as a percent)	(0.20%)
August 2019 Settlement Agreement | WG | Natural gas rates | 2020 rates | Tax Cuts and Jobs Act of 2017
Public Utilities, General Disclosures [Line Items]
Amortization of regulatory liabilities	$ 3
August 2019 Settlement Agreement | WG | Natural gas rates | 2021 rates | Tax Cuts and Jobs Act of 2017
Public Utilities, General Disclosures [Line Items]
Amortization of regulatory liabilities	$ 3
August 2019 Settlement Agreement | WPS | 2020 and 2021 rates
Public Utilities, General Disclosures [Line Items]
Requested return on equity (as a percent)	10.00%
Requested common equity component average (as a percent)	52.50%
August 2019 Settlement Agreement | WPS | Electric rates | Earnings sharing mechanisms
Public Utilities, General Disclosures [Line Items]
Amortization period	2 years
August 2019 Settlement Agreement | WPS | Electric rates | 2020 rates
Public Utilities, General Disclosures [Line Items]
Requested rate increase	$ 35
Requested rate increase (as a percent)	3.50%
August 2019 Settlement Agreement | WPS | Electric rates | 2020 rates | Tax Cuts and Jobs Act of 2017
Public Utilities, General Disclosures [Line Items]
Amortization of regulatory liabilities	$ 11
August 2019 Settlement Agreement | WPS | Electric rates | 2021 rates | Tax Cuts and Jobs Act of 2017
Public Utilities, General Disclosures [Line Items]
Amortization of regulatory liabilities	39
August 2019 Settlement Agreement | WPS | Electric rates | 2020 and 2021 rates | Earnings sharing mechanisms
Public Utilities, General Disclosures [Line Items]
Amortization of regulatory liabilities	21
August 2019 Settlement Agreement | WPS | Natural gas rates | 2020 rates
Public Utilities, General Disclosures [Line Items]
Requested rate increase	$ 4
Requested rate increase (as a percent)	1.40%
August 2019 Settlement Agreement | WPS | Natural gas rates | 2020 rates | Tax Cuts and Jobs Act of 2017
Public Utilities, General Disclosures [Line Items]
Amortization of regulatory liabilities	$ 5
August 2019 Settlement Agreement | WPS | Natural gas rates | 2021 rates | Tax Cuts and Jobs Act of 2017
Public Utilities, General Disclosures [Line Items]
Amortization of regulatory liabilities	$ 5
March 2019 Rate Application | Electric rates | Tax Cuts and Jobs Act of 2017
Public Utilities, General Disclosures [Line Items]
Amortization period		40 years
Period of time over which a significant amount of refunds would be made		2 years
March 2019 Rate Application | Natural gas rates | Tax Cuts and Jobs Act of 2017
Public Utilities, General Disclosures [Line Items]
Amortization period		40 years
Period of time over which a significant amount of refunds would be made		2 years
March 2019 Rate Application | WE | 2020 and 2021 rates
Public Utilities, General Disclosures [Line Items]
Requested return on equity (as a percent)		10.35%
Requested common equity component average (as a percent)		52.00%
March 2019 Rate Application | WE | Electric rates | 2020 rates
Public Utilities, General Disclosures [Line Items]
Requested rate increase		$ 83
Requested rate increase (as a percent)		2.90%
March 2019 Rate Application | WE | Electric rates | 2020 rates | Tax Cuts and Jobs Act of 2017
Public Utilities, General Disclosures [Line Items]
Amortization of regulatory liabilities		$ 94
March 2019 Rate Application | WE | Electric rates | 2021 rates
Public Utilities, General Disclosures [Line Items]
Requested rate increase		$ 83
Requested rate increase (as a percent)		2.90%
March 2019 Rate Application | WE | Electric rates | 2021 rates | Tax Cuts and Jobs Act of 2017
Public Utilities, General Disclosures [Line Items]
Amortization of regulatory liabilities		$ 17
March 2019 Rate Application | WE | Natural gas rates | 2020 rates
Public Utilities, General Disclosures [Line Items]
Requested rate increase		$ 15
Requested rate increase (as a percent)		3.90%
March 2019 Rate Application | WE | Steam rates | 2020 rates
Public Utilities, General Disclosures [Line Items]
Requested rate increase		$ 1
Requested rate increase (as a percent)		4.50%
March 2019 Rate Application | WG | 2020 and 2021 rates
Public Utilities, General Disclosures [Line Items]
Requested return on equity (as a percent)		10.30%
Requested common equity component average (as a percent)		52.00%
March 2019 Rate Application | WG | Natural gas rates | 2020 rates
Public Utilities, General Disclosures [Line Items]
Requested rate increase		$ 11
Requested rate increase (as a percent)		1.80%
March 2019 Rate Application | WPS | 2020 and 2021 rates
Public Utilities, General Disclosures [Line Items]
Requested return on equity (as a percent)		10.35%
Requested common equity component average (as a percent)		52.00%
March 2019 Rate Application | WPS | Electric rates | 2020 rates
Public Utilities, General Disclosures [Line Items]
Requested rate increase		$ 49
Requested rate increase (as a percent)		4.90%
March 2019 Rate Application | WPS | Electric rates | 2020 rates | Tax Cuts and Jobs Act of 2017
Public Utilities, General Disclosures [Line Items]
Amortization of regulatory liabilities		$ 16
March 2019 Rate Application | WPS | Electric rates | 2020 rates | Earnings sharing mechanisms
Public Utilities, General Disclosures [Line Items]
Amortization of regulatory liabilities		21
March 2019 Rate Application | WPS | Electric rates | 2021 rates
Public Utilities, General Disclosures [Line Items]
Requested rate increase		$ 49
Requested rate increase (as a percent)		4.90%
March 2019 Rate Application | WPS | Electric rates | 2021 rates | Tax Cuts and Jobs Act of 2017
Public Utilities, General Disclosures [Line Items]
Amortization of regulatory liabilities		$ 24
March 2019 Rate Application | WPS | Natural gas rates | 2020 rates
Public Utilities, General Disclosures [Line Items]
Requested rate increase		$ 7
Requested rate increase (as a percent)		2.40%
March 2019 Rate Application | WPS | Natural gas rates | 2020 rates | Tax Cuts and Jobs Act of 2017
Public Utilities, General Disclosures [Line Items]
Amortization of regulatory liabilities		$ 7
March 2019 Rate Application | WPS | Natural gas rates | 2021 rates
Public Utilities, General Disclosures [Line Items]
Requested rate increase		$ 7
Requested rate increase (as a percent)		2.40%