Benefit Plans (Net Periodic Benefit Cost (Income)) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Pension [Member]
Contributions by employer	$ 7.5	$ 9.8
Service cost	1.3	1.1
Interest cost	2.4	2.0
Expected return on assets	(4.0)	(3.7)
Prior service cost	0.2	0.2
Actuarial loss / (gain)	1.4	2.3
Net periodic benefit cost	1.3	1.9
Postretirement [Member]
Defined Benefit Plan, Funded (Unfunded) Status of Plan	8.8		$ 8.9
Subsidiaries [Member] | Pension [Member]
Contributions by employer	7.5	9.8
Service cost	1.3	1.1
Interest cost	2.4	2.0
Expected return on assets	(4.0)	(3.7)
Prior service cost	0.3	0.3
Actuarial loss / (gain)	1.9	2.8
Net periodic benefit cost	1.9	$ 2.5
Subsidiaries [Member] | Postretirement [Member]
Defined Benefit Plan, Funded (Unfunded) Status of Plan	$ 8.8		$ 8.9