Components of Accrued Revenue (Detail) - USD ($) $ in Millions		Dec. 31, 2023	Dec. 31, 2022
Deferred Revenue Arrangement [Line Items]
Regulatory Assets – Current	[1]	$ 56.5	$ 66.5
Total Accrued Revenue		63.4	72.8
Unbilled Revenues
Deferred Revenue Arrangement [Line Items]
Regulatory Assets – Current		6.9	6.3
Regulatory Assets
Deferred Revenue Arrangement [Line Items]
Regulatory Assets – Current		$ 56.5	$ 66.5

[1] Reflects amounts included in Accrued Revenue on the Company’s Consolidated Balance Sheets.