Summary of Significant Accounting Policies Property, Plant and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
PWGS | Minimum
Property, plant, and equipment
Estimated useful life	10 years
PWGS | Maximum
Property, plant, and equipment
Estimated useful life	45 years
ERGS | Minimum
Property, plant, and equipment
Estimated useful life	10 years
ERGS | Maximum
Property, plant, and equipment
Estimated useful life	55 years
Software | Minimum
Property, plant, and equipment
Estimated useful life	3 years
Software | Maximum
Property, plant, and equipment
Estimated useful life	15 years
WE
Property, plant, and equipment
Annual utility composite depreciation rate (as a percent)	3.19%	3.11%	3.18%
WPS
Property, plant, and equipment
Annual utility composite depreciation rate (as a percent)	2.63%	2.44%	2.50%
WG
Property, plant, and equipment
Annual utility composite depreciation rate (as a percent)	2.33%	2.29%	2.30%
PGL
Property, plant, and equipment
Annual utility composite depreciation rate (as a percent)	3.16%	3.20%	3.25%
NSG
Property, plant, and equipment
Annual utility composite depreciation rate (as a percent)	2.48%	2.48%	2.45%
MERC
Property, plant, and equipment
Annual utility composite depreciation rate (as a percent)	2.47%	2.33%	1.95%
Reduction in Depreciation Expense Related to Depreciation Study			$ 1.4
MGU
Property, plant, and equipment
Annual utility composite depreciation rate (as a percent)	2.67%	2.54%	2.61%
UMERC
Property, plant, and equipment
Annual utility composite depreciation rate (as a percent)	2.97%	2.87%	2.50%