Benefit Plans (Tables)

6 Months Ended

Jun. 30, 2021

Entity Information [Line Items]

Schedule of Net Periodic Benefit Cost / (Income)

The net periodic benefit cost of the pension benefit plans for the three and six months ended June 30, 2021 and 2020 was:

	Three months ended				Six months ended
	June 30,				June 30,
$ in millions	2021		2020		2021		2020
Service cost	$	1.1	$	1.0	$	2.2	$	1.9
Interest cost	2.0		2.9		4.0		5.9
Expected return on plan assets	(3.7)		(4.7)		(7.4)		(9.4)
Amortization of unrecognized:
Prior service cost	0.2		0.2		0.4		0.5
Actuarial loss	2.3		1.6		4.6		3.1
Net periodic benefit cost	$	1.9	$	1.0	$	3.8	$	2.0

Subsidiaries [Member]

Entity Information [Line Items]

Schedule of Net Periodic Benefit Cost / (Income)

The net periodic benefit cost of the pension benefit plans for the three and six months ended June 30, 2021 and 2020 was:

	Three months ended				Six months ended
	June 30,				June 30,
$ in millions	2021		2020		2021		2020
Service cost	$	1.1	$	1.0	$	2.2	$	1.9
Interest cost	2.0		2.9		4.0		5.9
Expected return on plan assets	(3.7)		(4.7)		(7.4)		(9.4)
Amortization of unrecognized:
Prior service cost	0.3		0.4		0.6		0.7
Actuarial loss	2.8		2.1		5.6		4.3
Net periodic benefit cost	$	2.5	$	1.7	$	5.0	$	3.4