Employee Benefit Plans (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined contribution plan operating expenses within discontinued operations		$ 23
Defined contribution plan operating expenses within discontinued operations after tax		17
Defined contribution plan other operations and maintenance expense		13
Defined contribution plan other operations and maintenance expense after tax		10
Expected contributions to qualified defined benefit pension plans for remainder of fiscal year	$ 22
East Ohio
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Remeasured pension and other postretirement benefit plans amount		202
Remeasured pension and other postretirement benefit plans after tax amount		151
Discontinued Operations
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost		3
Non-service cost (credit)		14
Other Postretirement Benefits Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	3	3
Other Postretirement Benefits Plan | Minimum | East Ohio
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Remeasurement, discount rate			5.61%
Other Postretirement Benefits Plan | Maximum | East Ohio
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Remeasurement, discount rate			5.62%
Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Contributions to qualified defined benefit pension plans	1
Service cost	$ 19	$ 22
Pension Benefits | East Ohio
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Remeasurement, discount rate		5.62%