Employee Benefit Plans (Fair Values of Pension and Post Retirement Plan Assets by Asset Category) (Parenthetical) (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Common stock	$ 0	$ 365,000,000
Preferred stock	258,000,000
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Pending sales of securities	35,000,000
Pending sales of securities and advanced subscriptions		198,000,000
Net accrued income	27,000,000	20,000,000
Pending purchases of securities	62,000,000	71,000,000
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Pending sales of securities	5,000,000	10,000,000
Net accrued income	2,000,000	2,000,000
Pending purchases of securities	$ 3,000,000	$ 2,000,000