Employee Benefit Plans and Equity Compensation Plan (Amounts Recognized in Regulatory Assets) (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	$ 70	$ 114
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	$ (5)	$ 1

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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