Components of Accrued Revenue (Detail) - USD ($) $ in Millions		Dec. 31, 2022	Dec. 31, 2021
Deferred Revenue Arrangement [Line Items]
Regulatory Assets – Current	[1]	$ 66.5	$ 47.4
Total Accrued Revenue		72.8	61.2
Unbilled Revenues
Deferred Revenue Arrangement [Line Items]
Regulatory Assets – Current		6.3	13.8
Regulatory Assets
Deferred Revenue Arrangement [Line Items]
Regulatory Assets – Current		$ 66.5	$ 47.4

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