Benefit Plans (Net Periodic Benefit Cost (Income)) (Details) - Pension [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Contributions by employer			$ 7.5	$ 7.5
Service cost	$ 0.7	$ 0.8	1.9	2.2
Interest cost	3.6	3.9	11.0	11.9
Expected return on assets	(3.7)	(4.4)	(11.1)	(13.2)
Prior service cost	0.2	0.3	0.7	0.8
Actuarial loss / (gain)	0.5	0.2	1.6	0.5
Net periodic benefit cost	1.3	0.8	4.1	2.2
Subsidiaries [Member]
Contributions by employer			7.5	7.5
Service cost	0.7	0.8	1.9	2.2
Interest cost	3.6	3.9	11.0	11.9
Expected return on assets	(3.7)	(4.4)	(11.1)	(13.2)
Prior service cost	0.3	0.2	0.7	0.8
Actuarial loss / (gain)	0.9	0.3	2.9	0.9
Net periodic benefit cost	$ 1.8	$ 0.8	$ 5.4	$ 2.6