Benefit Plans (Net Periodic Benefit Cost (Income)) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Pension [Member]
Contributions by employer	$ 7.5	$ 7.5
Service cost	0.7	1.3
Interest cost	4.0	2.4
Expected return on assets	(4.4)	(4.0)
Prior service cost	0.2	0.2
Actuarial loss / (gain)	0.2	1.4
Net periodic benefit cost	0.7	1.3
Postretirement [Member]
Defined Benefit Plan, Funded (Unfunded) Status of Plan	7.1		$ 7.0
Subsidiaries [Member] | Pension [Member]
Contributions by employer	7.5	7.5
Service cost	0.7	1.3
Interest cost	4.0	2.4
Expected return on assets	(4.4)	(4.0)
Prior service cost	0.3	0.3
Actuarial loss / (gain)	0.3	1.9
Net periodic benefit cost	0.9	$ 1.9
Subsidiaries [Member] | Postretirement [Member]
Defined Benefit Plan, Funded (Unfunded) Status of Plan	$ 7.1		$ 7.0