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Differences Between Provisions for Income Taxes and Provisions Calculated at Statutory Federal Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Examination [Line Items]
Statutory Federal Income Tax Rate	21.00%	34.00%	34.00%
State Income Taxes, net	6.00%	6.00%	4.00%
Utility Plant Differences	(7.00%)	(1.00%)	(1.00%)
Tax Credits and Other, net		(1.00%)	(1.00%)
Effective Income Tax Rate	20.00%	38.00%	36.00%

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- Definition

Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to state and local income tax expense (benefit), net of federal tax expense (benefit).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to tax credits and other adjustments. Including, but not limited to, research credit, foreign tax credit, investment tax credit, and other tax credits.

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