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Common Equity - Dividend Restrictions (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2017
USD ($)
period
Dec. 31, 2016
Dividend Payment Restrictions [Line Items]    
Junior notes minimum interest deferral payment period (in periods) | period 1  
Junior notes maximum interest payment deferral period (in years) 10 years  
Restricted net assets of consolidated subsidiaries $ 6,300  
Undistributed earnings of investees accounted for by the equity method $ 355  
Percentage of restricted net assets of subsidiaries and equity method investments that triggers dividend restriction disclosures 25.00%  
WE | $100 par value, Serial Preferred Stock, 3.60% series redeemable    
Dividend Payment Restrictions [Line Items]    
Preferred Stock, dividend rate (as a percent) 3.60% 3.60%
WE | $100 par value, Serial Preferred Stock, 3.60% series redeemable | Common stock equity to total capitalization is less than 25%    
Dividend Payment Restrictions [Line Items]    
Percentage of common equity to total capitalization required to be maintained 25.00%  
WE | $100 par value, Serial Preferred Stock, 3.60% series redeemable | Common stock equity to total capitalization is less than 20%    
Dividend Payment Restrictions [Line Items]    
Percentage of common equity to total capitalization required to be maintained 20.00%  
WE | Minimum | Public Service Commission of Wisconsin    
Dividend Payment Restrictions [Line Items]    
Common equity ratio required to be maintained (as a percent) 51.00%  
WE | Maximum | $100 par value, Serial Preferred Stock, 3.60% series redeemable | Common stock equity to total capitalization is less than 25%    
Dividend Payment Restrictions [Line Items]    
Percentage of net income for which dividends can be declared 75.00%  
WE | Maximum | $100 par value, Serial Preferred Stock, 3.60% series redeemable | Common stock equity to total capitalization is less than 20%    
Dividend Payment Restrictions [Line Items]    
Percentage of net income for which dividends can be declared 50.00%  
WG | Minimum | Public Service Commission of Wisconsin    
Dividend Payment Restrictions [Line Items]    
Common equity ratio required to be maintained (as a percent) 49.50%  
WPS | Minimum | Public Service Commission of Wisconsin    
Dividend Payment Restrictions [Line Items]    
Common equity ratio required to be maintained (as a percent) 51.00%