REGULATORY ENVIRONMENT (Details) $ in Millions	1 Months Ended
	Apr. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Jan. 31, 2017	Oct. 31, 2016 USD ($)	Aug. 31, 2016 USD ($) MW	Apr. 30, 2015 USD ($)
WE, WG, and WPS | Natural gas storage facility in Michigan
Regulatory environment
Percentage of natural gas storage needs provided by the facility			33.33%
PGL | Illinois Commerce Commission (ICC)
Regulatory environment
Number of years code of conduct reports must be provided to the ICC		4 years
Number of years quality assurance reports must be provided to the ICC		4 years
Amount of assurance that PGL's QIP rider costs will be recoverable		0
MERC | Minnesota Public Utilities Commission (MPUC) | 2016 rates | Natural gas rates
Regulatory environment
Approved rate increase				$ 6.8
Approved rate increase (as a percent)				3.00%
Approved return on equity (as a percent)				9.11%
Approved common equity component average (as a percent)				50.32%
Number of years decoupling mechanism authorized for use				3 years
Interim rate refund		$ 4.1
UMERC
Regulatory environment
Term of electric power purchase agreement (in years)					20 years
Capacity of natural gas-fired generation facility (in megawatts) | MW					180
Estimated cost of constructing a power plant					$ 265.0
Estimated cost of constructing a power plant, including AFUDC					$ 275.0
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%
UMERC | Michigan Public Service Commission (MPSC) | 2015 rates | Electric rates
Regulatory environment
Approved rate increase						$ 4.0
Approved return on equity (as a percent)						10.20%
Approved common equity component average (as a percent)						50.48%
Period of rate implementation (in years)						3 years
Subsequent event | WE, WG, and WPS | Public Service Commission of Wisconsin (PSCW) | 2018 and 2019 rates
Regulatory environment
Authorized revenue requirement for ReACT	$ 275.0
Number of utilities with earnings sharing mechanism	3
Percentage of first 50 basis points of additional utility earnings shared with customers	50.00%
ROE in excess of authorized amount (as a percent)	0.50%