Summary of Significant Accounting Policies Property, Plant and Equipment (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
PWGS | Minimum
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful life	10 years
PWGS | Maximum
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful life	45 years
ERGS | Minimum
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful life	10 years
ERGS | Maximum
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful life	55 years
Software | Minimum
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Software | Maximum
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful life	15 years
WE
Public Utility, Property, Plant and Equipment [Line Items]
Annual utility composite depreciation rate (as a percent)	3.00%	3.01%	2.93%
WPS
Public Utility, Property, Plant and Equipment [Line Items]
Annual utility composite depreciation rate (as a percent)	2.58%	1.30%
WG
Public Utility, Property, Plant and Equipment [Line Items]
Annual utility composite depreciation rate (as a percent)	2.34%	2.36%	2.69%
PGL
Public Utility, Property, Plant and Equipment [Line Items]
Annual utility composite depreciation rate (as a percent)	3.31%	1.67%
NSG
Public Utility, Property, Plant and Equipment [Line Items]
Annual utility composite depreciation rate (as a percent)	2.44%	1.22%
MERC
Public Utility, Property, Plant and Equipment [Line Items]
Annual utility composite depreciation rate (as a percent)	2.53%	1.26%
MGU
Public Utility, Property, Plant and Equipment [Line Items]
Annual utility composite depreciation rate (as a percent)	2.63%	1.32%