Employee Benefit Plans (Fair Values of Pension and Post Retirement Plan Assets by Asset Category) (Parenthetical) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Preferred stock	$ 0	$ 170
Pending sales of securities and advanced subscriptions	298	177
Net accrued income	24	27
Pending purchases of securities	54	180
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Preferred stock	0	10
Pending sales of securities and advanced subscriptions	17	10
Net accrued income	2	2
Pending purchases of securities	$ 2	$ 10