Summary of Significant Accounting Policies Accounting Records (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Regulatory Assets, Current	$ 182.6	$ 19.8
Regulatory Assets, Noncurrent	1,230.8	415.6
Deferred Storm and Property Reserve Deficiency, Current	2.7
Regulatory Liability, Current	2.5	35.1
Pension Plans, Defined Benefit [Member] | Defined Benefit Plans Income Loss [Member]
Components of Benefit Obligation Regulatory Asset	89.6	147.3
Other Postretirement Benefit Plans, Defined Benefit [Member] | Defined Benefit Plans Income Loss [Member]
Components of Benefit Obligation Regulatory Asset	23.2	26.2
Other Postretirement Benefit Plans, Defined Benefit [Member] | Prior Service Cost [Member]
Components of Benefit Obligation Regulatory Asset	$ (3.6)	$ (8.6)