Regulatory Environment (Details) $ in Millions	1 Months Ended												3 Months Ended	12 Months Ended
	May 31, 2018 USD ($) MW solar_projects	Mar. 31, 2018 USD ($)	Feb. 28, 2018 USD ($) Filings	Dec. 31, 2017 USD ($)	Nov. 30, 2017 USD ($)	Oct. 31, 2017 wind_turbines utility MW	Sep. 30, 2017 USD ($) utility	Jan. 31, 2017	Oct. 31, 2016 USD ($)	Aug. 31, 2016 MW	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2018 USD ($) customer Assurance	Dec. 31, 2018 USD ($) customer change Assurance	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Regulatory environment
AFUDC														$ 6.9	$ 4.9	$ 10.9
WE
Regulatory environment
AFUDC														$ 1.5	1.2	1.7
WE | Public Service Commission of Wisconsin (PSCW) | 2018 and 2019 Rates
Regulatory environment
Approved return on equity (as a percent)							10.20%
Income Statement impact of flow through of repair related deferred tax liabilities | change														0
WE | Public Service Commission of Wisconsin (PSCW) | 2018 and 2019 Rates | Electric rates
Regulatory environment
Percentage of current tax benefit from Tax Cuts and Jobs Act of 2017 to be used to reduce regulatory assets	80.00%
Percent of current tax benefit from Tax Cuts and Jobs Act of 2017 to be returned to customers via bill credits	20.00%
WE | MichiganPublicServiceCommissionMPSC [Member]
Regulatory environment
Number of Electric Customers Served in Michigan | customer													1	1
WG | Public Service Commission of Wisconsin (PSCW) | 2018 and 2019 Rates
Regulatory environment
Approved return on equity (as a percent)							10.30%
WPS
Regulatory environment
AFUDC														$ 1.9	1.6	$ 8.1
WPS | Forward Wind Energy Center
Regulatory environment
Number of utilities, along with WPS, that entered in an agreement to purchase Forward Wind Energy Center | utility						2
Number of wind turbines at Forward Wind Energy Center | wind_turbines						86
Capacity of Forward Wind Energy Center | MW						138
WPS | Public Service Commission of Wisconsin (PSCW) | Two Creeks Solar Farm [Member]
Regulatory environment
WPS individual ownership interest | MW	100
WPS | Public Service Commission of Wisconsin (PSCW) | Badger Hollow and Two Creeks Solar Farms [Member]
Regulatory environment
Number of Solar Projects in WI that WPS Filed with the PSCW to Acquire an Interest In | solar_projects	2
WPS Total Ownership Capacity in Badger Hollow and Two Creeks | MW	200
WPS Total Share of Cost of Badger Hollow and Two Creeks	$ 260.0
WPS | Public Service Commission of Wisconsin (PSCW) | Badger Hollow Solar Farm [Member]
Regulatory environment
WPS individual ownership interest | MW	100
WPS | Public Service Commission of Wisconsin (PSCW) | 2018 and 2019 Rates
Regulatory environment
Approved return on equity (as a percent)							10.00%
Authorized revenue requirement for the ReACT project							$ 275.0
AFUDC														51.0
Estimated cost of the ReACT project, excluding AFUDC														$ 342.0
WPS | Public Service Commission of Wisconsin (PSCW) | 2018 and 2019 Rates | Electric rates
Regulatory environment
Percentage of current tax benefit from Tax Cuts and Jobs Act of 2017 to be used to reduce regulatory assets	40.00%
Percent of current tax benefit from Tax Cuts and Jobs Act of 2017 to be returned to customers via bill credits	60.00%
WPS | Public Service Commission of Wisconsin (PSCW) | 2016 Rates
Regulatory environment
Approved return on equity (as a percent)												10.00%
Approved common equity component average (as a percent)												51.00%
WPS | Public Service Commission of Wisconsin (PSCW) | 2016 Rates | Electric rates
Regulatory environment
Authorized revenue requirement for the ReACT project											$ 275.0	$ 275.0
Approved rate increase (decrease)												$ (7.9)
Approved rate increase (decrease), percentage												(0.80%)
Percent fuel costs can vary from the rate case approved costs before deferral is required												2.00%
WPS | Public Service Commission of Wisconsin (PSCW) | 2016 Rates | Natural gas rates
Regulatory environment
Approved rate increase (decrease)												$ (6.2)
Approved rate increase (decrease), percentage												(2.10%)
WE, WG, and WPS | Public Service Commission of Wisconsin (PSCW) | Natural gas storage facilities in Michigan
Regulatory environment
Percentage of natural gas storage needs provided by the facilities								33.33%
WE, WG, and WPS | Public Service Commission of Wisconsin (PSCW) | 2018 and 2019 Rates
Regulatory environment
ActualROEInExcessOfAuthorizedAmount							0.50%
Number of utilities with earnings sharing mechanism | utility							3
Percentage of first 50 basis points of additional utility earnings shared with customers							50.00%
WE, WG, and WPS | Public Service Commission of Wisconsin (PSCW) | 2018 and 2019 Rates | Natural gas rates
Regulatory environment
Percent of current tax benefit from Tax Cuts and Jobs Act of 2017 to be returned to customers via bill credits	100.00%
Michigan Gas Utilities Corporation and Upper Michigan Energy Resources Corporation [Member] | MichiganPublicServiceCommissionMPSC [Member]
Regulatory environment
Number of filings required related to the Tax Cuts and Jobs Act of 2018 | Filings			3
PGL | Illinois Commerce Commission (ICC)
Regulatory environment
Amount of rate base reduction as a result of a settlement			$ 5.4
Amount to be refunded to ratepayers as a result of a settlement			$ 4.7
Amount of assurance that costs incurred under QIP rider are recoverable | Assurance													0	0
MERC | Minnesota Public Utilities Commission (MPUC) | 2018 Rates | Natural gas rates
Regulatory environment
Approved return on equity (as a percent)													9.70%
Approved rate increase (decrease)													$ 3.1
Approved rate increase (decrease), percentage													1.26%
Approved common equity component average (as a percent)													50.90%
Interim rate increase		$ 7.0			$ 9.5
Interim rate increase (as a percent)		2.81%			3.78%
Interim Rate Reduction		$ 2.5
Interim rates return on equity (as a percent)		9.11%
Interim rates common equity component average (as a percent)		50.90%
MERC | Minnesota Public Utilities Commission (MPUC) | 2016 Rates | Natural gas rates
Regulatory environment
Approved return on equity (as a percent)									9.11%
Approved rate increase (decrease)									$ 6.8
Approved rate increase (decrease), percentage									3.00%
Approved common equity component average (as a percent)									50.32%
Number of years decoupling mechanism authorized for use									3 years
Interim rates refunded to customers													$ 4.1	$ 4.1
MGU | Michigan Public Service Commission (MPSC) | 2016 Rates | Natural gas rates
Regulatory environment
Approved return on equity (as a percent)												9.90%
Approved rate increase (decrease)												$ 3.4
Approved rate increase (decrease), percentage												2.40%
Approved common equity component average (as a percent)												52.00%
UMERC
Regulatory environment
AFUDC														2.4	$ 0.1
Term of electric power purchase agreement (in years)										20 years
Capacity of natural gas-fired generation facility (in megawatts) | MW						180				180
Estimated cost of constructing power plant														266.0
Estimated cost of constructing a power plant, including AFUDC														$ 277.0
Portion of the power plant costs recoverable from Tilden Mining Company (as a percent)						50.00%
Portion of the power plant costs recoverable from utility customers (as a percent)						50.00%
Utility operations | Tax Cuts and Jobs Act of 2017
Regulatory environment
Change in deferred income taxes from tax legislation				$ 2,450.0