Benefit Plans (Net Periodic Benefit Cost (Income)) (Details) - Pension [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Contributions by employer	$ 0.0	$ 7.5
Service cost	0.6	0.6
Interest cost	3.6	3.7
Expected return on assets	(3.9)	(3.7)
Prior service cost	0.2	0.3
Actuarial loss / (gain)	0.8	0.5
Net periodic benefit cost	1.3	1.4
Subsidiaries [Member]
Service cost	0.6	0.6
Interest cost	3.6	3.7
Expected return on assets	(3.9)	(3.7)
Prior service cost	0.2	0.2
Actuarial loss / (gain)	1.3	1.0
Net periodic benefit cost	$ 1.8	$ 1.8