Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2023

Related Party Transaction [Line Items]

Schedule of Accumulated Other Comprehensive Income (Loss)

The changes in the components of AOCL during the three months ended March 31, 2023 are as follows:

$ in millions	Change in cash flow hedges		Change in unfunded pension and other postretirement obligations		Total
Balance as of January 1, 2023	$	12.0	$	(14.4)	$	(2.4)
Amounts reclassified from AOCL to earnings	(0.2)		—		(0.2)
Balance as of March 31, 2023	$	11.8	$	(14.4)	$	(2.6)

Reclassification out of Accumulated Other Comprehensive Income

The amounts reclassified out of AOCL by component during the three months ended March 31, 2023 and 2022 are as follows:

Details about AOCL components	Affected line item in the Condensed Consolidated Statements of Operations	Three months ended
		March 31,
$ in millions		2023		2022
Net gains on cash flow hedges (Note 4):
	Interest expense	$	(0.2)	$	(0.2)
	Income tax effect	—		0.1
	Net of income taxes	(0.2)		(0.1)
Amortization of unfunded pension and other postretirement obligations (Note 7):
	Other expense	—		0.3
	Income tax effect	—		(0.1)
	Net of income taxes	—		0.2
Total reclassifications for the period, net of income taxes		$	(0.2)	$	0.1

Schedule of Supplemental Financial Information

The following table summarizes accounts receivable as of March 31, 2023 and December 31, 2022:

	March 31,		December 31,
$ in millions	2023		2022
Accounts receivable, net:
Customer receivables	$	68.3	$	61.3
Unbilled revenue	18.2		24.0
Amounts due from affiliates	3.8		3.2
Other	7.0		3.9
Allowance for credit losses	(0.6)		(0.5)
Total accounts receivable, net	$	96.7	$	91.9

Accounts Receivable, Allowance for Credit Loss

The following table is a roll forward of our allowance for credit losses related to the accounts receivable balances for the three months ended March 31, 2023 and 2022:

$ in millions	Beginning Allowance Balance		Current Period Provision		Write-offs Charged Against Allowances		Recoveries Collected		Ending Allowance Balance
2023	$	0.5	$	0.9	$	(1.1)	$	0.3	$	0.6
2022	$	0.3	$	(0.1)	$	(0.2)	$	0.2	$	0.2

The allowance for credit losses primarily relates to utility customer receivables, including unbilled amounts. Expected credit loss estimates are developed by disaggregating customers into those with similar credit risk characteristics and using historical credit loss experience. In addition, we also consider how current and future economic conditions are expected to impact collectability. Amounts are written off when reasonable collections efforts have been exhausted.

New Accounting Pronouncements, Policy [Policy Text Block]

New Accounting Pronouncements Adopted in 2023

We have assessed and determined that the new accounting pronouncements adopted did not have a material impact on our consolidated financial statements.

New Accounting Pronouncements Issued But Not Yet Effective

We have assessed and determined that the new accounting pronouncements issued but not yet effective are not expected to have a material impact on our consolidated financial statements.

Schedule of Cash and Cash Equivalents [Table Text Block]

The following table summarizes cash, cash equivalents, and restricted cash amounts reported on the Condensed Consolidated Balance Sheets that reconcile to the total of such amounts as shown on the Condensed Consolidated Statements of Cash Flows:

$ in millions	March 31, 2023		December 31, 2022
Cash and cash equivalents	$	21.0	$	30.5
Restricted cash (included in Prepayments and other current assets)	0.1		0.1
Cash, Cash Equivalents, and Restricted Cash, End of Period	$	21.1	$	30.6

Schedule of New Accounting Pronouncements

New Accounting Pronouncements Issued But Not Yet Effective

We have assessed and determined that the new accounting pronouncements issued but not yet effective are not expected to have a material impact on our consolidated financial statements.

Subsidiaries [Member]

Related Party Transaction [Line Items]

Schedule of Accumulated Other Comprehensive Income (Loss)

The changes in the components of AOCL during the three months ended March 31, 2023 are as follows:

$ in millions	Change in Accumulated other comprehensive loss
Balance as of January 1, 2023	$	(26.8)
Amounts reclassified from AOCL to earnings	0.1
Balance as of March 31, 2023	$	(26.7)

Reclassification out of Accumulated Other Comprehensive Income

AOCL by component during the three months ended March 31, 2023 and 2022 are as follows:

Details about AOCL components	Affected line item in the Condensed Statements of Operations	Three months ended
		March 31,
$ in millions		2023		2022
Amortization of unfunded pension and other postretirement obligations (Note 6):
	Other expense	0.2		0.9
	Income tax effect	(0.1)		(0.2)
	Net of income taxes	0.1		0.7
Total reclassifications for the period, net of income taxes		$	0.1	$	0.7

Schedule of Supplemental Financial Information

The following table summarizes accounts receivable as of March 31, 2023 and December 31, 2022:

	March 31,		December 31,
$ in millions	2023		2022
Accounts receivable, net:
Customer receivables	67.6		$	60.6
Unbilled revenue	18.2		24.0
Amounts due from affiliates	4.5		4.4
Other	6.9		3.8
Allowance for credit losses	(0.6)		(0.5)
Total accounts receivable, net	$	96.6	$	92.3

Accounts Receivable, Allowance for Credit Loss

The following table is a roll forward of our allowance for credit losses related to the accounts receivable balances for the three months ended March 31, 2023 and 2022:

$ in millions	Beginning Allowance Balance		Current Period Provision		Write-offs Charged Against Allowances		Recoveries Collected		Ending Allowance Balance
2023	$	0.5	$	0.9	$	(1.1)	$	0.3	$	0.6
2022	$	0.3	$	(0.1)	$	(0.2)	$	0.2	$	0.2

The allowance for credit losses primarily relates to utility customer receivables, including unbilled amounts. Expected credit loss estimates are developed by disaggregating customers into those with similar credit risk characteristics and using historical credit loss experience. In addition, we also consider how current and future economic conditions are expected to impact collectability. Amounts are written off when reasonable collections efforts have been exhausted.

New Accounting Pronouncements, Policy [Policy Text Block]

New Accounting Pronouncements Adopted in 2023

We have assessed and determined that the new accounting pronouncements adopted did not have a material impact on our consolidated financial statements.

New Accounting Pronouncements Issued But Not Yet Effective

We have assessed and determined that the new accounting pronouncements issued but not yet effective are not expected to have a material impact on our financial statements.

Schedule of Cash and Cash Equivalents [Table Text Block]

The following table summarizes cash, cash equivalents, and restricted cash amounts reported on the Condensed Balance Sheets that reconcile to the total of such amounts as shown on the Condensed Statements of Cash Flows:

$ in millions	March 31, 2023		December 31, 2022
Cash and cash equivalents	$	9.4	$	19.7
Restricted cash (included in Prepayments and other current assets)	0.1		0.1
Cash, Cash Equivalents, and Restricted Cash, End of Period	$	9.5	$	19.8