Employee Benefit Plans (Narrative) (Detail) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2021
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Contributions to qualified defined benefit pension plans and OPEB plans	$ 0		$ 0
Other Postretirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 6,000,000	$ 7,000,000	$ 12,000,000	$ 14,000,000
Other Postretirement Benefits | Scenario Forecast
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Contribution to voluntary employees beneficiary association					$ 0
Discontinued Operations
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost		$ 4,000,000		$ 9,000,000