Pension and Other Postretirement Benefit Plans - Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income and Regulatory Assets or Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Net (Gain) Loss	$ 3.9	$ (32.7)
Amortization of Prior Service Cost	7.5	7.6
Amortization of Loss	(0.4)	(3.0)
Total Recognized in Other Comprehensive Income and Regulatory Assets or Liabilities	11.0	(28.1)
Pension [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Net (Gain) Loss	11.4	(20.1)
Amortization of Prior Service Cost	0.1	0.2
Prior Service Credit Arising During the Period	0.8	0.0
Amortization of Loss	(11.4)	(18.8)
Total Recognized in Other Comprehensive Income and Regulatory Assets or Liabilities	$ 0.9	$ (38.7)