Employee Benefits, Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Retirement Plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 2.6	$ 2.8	$ 3.0
Interest cost	2.1	2.7	3.9
Expected return on plan assets	(6.2)	(6.3)	(6.4)
Amortization of unrecognized net loss	0.8	1.9	2.2
Settlement charge	1.6	2.4	2.9
Regulatory asset decrease	2.5	0.0	0.0
Net periodic benefit cost	3.4	3.5	5.6
PBOP
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	0.1	0.1	0.1
Interest cost	0.9	1.1	1.4
Expected return on plan assets	(2.7)	(3.2)	(3.0)
Amortization of unrecognized net loss	0.0	0.0	0.0
Settlement charge	0.0	0.0	0.0
Net periodic benefit cost	$ (1.7)	$ (2.0)	$ (1.5)
Pension Plan
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Future rate recovery	in excess of $6.0 million