Benefit Plans (Net Periodic Benefit Cost (Income)) (Details) - Pension [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Contributions by employer			$ 7.5	$ 7.5
Service cost	$ 0.6	$ 0.7	1.2	1.4
Interest cost	3.7	4.0	7.4	8.0
Expected return on assets	(3.7)	(4.4)	(7.4)	(8.8)
Prior service cost	0.2	0.3	0.5	0.5
Actuarial loss / (gain)	0.6	0.1	1.1	0.3
Net periodic benefit cost	1.4	0.7	2.8	1.4
Subsidiaries [Member]
Contributions by employer			7.5	7.5
Service cost	0.6	0.7	1.2	1.4
Interest cost	3.7	4.0	7.4	8.0
Expected return on assets	(3.7)	(4.4)	(7.4)	(8.8)
Prior service cost	0.2	0.3	0.4	0.6
Actuarial loss / (gain)	1.0	0.3	2.0	0.6
Net periodic benefit cost	$ 1.8	$ 0.9	$ 3.6	$ 1.8