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