Benefit Plans (Net Periodic Benefit Cost (Income)) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Pension [Member]
Contributions by employer			$ 7.5	$ 7.5
Service cost	$ 0.8	$ 1.2	2.2	3.7
Interest cost	3.9	2.4	11.9	7.2
Expected return on assets	(4.4)	(4.0)	(13.2)	(11.9)
Prior service cost	0.3	0.3	0.8	0.8
Actuarial loss / (gain)	0.2	1.4	0.5	4.1
Net periodic benefit cost	0.8	1.3	2.2	3.9
Postretirement [Member]
Defined Benefit Plan, Funded (Unfunded) Status of Plan	6.6		6.6		$ 7.0
Subsidiaries [Member] | Pension [Member]
Contributions by employer			7.5	7.5
Service cost	0.8	1.2	2.2	3.7
Interest cost	3.9	2.4	11.9	7.2
Expected return on assets	(4.4)	(4.0)	(13.2)	(11.9)
Prior service cost	0.2	0.3	0.8	0.9
Actuarial loss / (gain)	0.3	2.0	0.9	5.8
Net periodic benefit cost	0.8	$ 1.9	2.6	$ 5.7
Subsidiaries [Member] | Postretirement [Member]
Defined Benefit Plan, Funded (Unfunded) Status of Plan	$ 6.6		$ 6.6		$ 7.0