Operating Revenues - Other Non-Utility Operating Revenues (Details) - Revenues from contracts with customers - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Operating Revenues
Revenues from contracts with customers	$ 7,169.3	$ 7,449.3	$ 7,680.3
Other non-utility revenues
Disaggregation of Operating Revenues
Revenues from contracts with customers	76.3	70.2	53.0
Other non-utility revenues | We Power revenues
Disaggregation of Operating Revenues
Revenues from contracts with customers	22.9	25.4	25.3
Other non-utility revenues | Distributed renewable solar project revenues
Disaggregation of Operating Revenues
Revenues from contracts with customers	1.4	4.0	8.0
Other non-utility revenues | Other
Disaggregation of Operating Revenues
Revenues from contracts with customers	0.3	0.2	0.2
Transferred over time | Other non-utility revenues | Wind generation revenues
Disaggregation of Operating Revenues
Revenues from contracts with customers	34.6	24.0	3.6
Transferred over time | Other non-utility revenues | Appliance service repairs
Disaggregation of Operating Revenues
Revenues from contracts with customers	$ 17.1	$ 16.6	$ 15.9