Summary of Significant Accounting Policies Stock-Based Compensation (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares of WEC Energy Group common stock authorized for issuance	34,300,000
Cumulative-effect from adoption of ASU 2016-09				$ 11.9
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)	3 years
Minimum exercise price of stock option as a percent of WEC Energy Group common stock fair value on the grant date	100.00%
Period after the grant date during which stock options can't be exercised (in months)	6 months
Maximum term of awards (in years)	10 years
Stock options granted (in shares)	59,404	81,730	80,770
Estimated weighted-average fair value per stock option (in dollars per share)	$ 8.60	$ 7.26	$ 7.12
Risk-free interest rate, minimum (as a percent)	2.50%	1.60%	0.70%
Risk-free interest rate, maximum (as a percent)	2.70%	2.50%	2.50%
Dividend yield (as a percent)	3.60%	3.50%	3.50%
Expected volatility (as a percent)	17.00%	18.00%	19.00%
Expected life (years)	8 years 6 months	5 years 1 month 6 days	6 years 2 months 12 days
Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)	3 years
Percentage to vest each year after the grant date	33.00%
Performance units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)	3 years
Performance units | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Payout ratio (as a percent)	0.00%
Performance units | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Payout ratio (as a percent)	175.00%