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Employee Benefit Plans (Narrative) (Detail) - USD ($)
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 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 $ 8,000,000 $ 18,000,000 $ 22,000,000  
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   $ 3,000,000   $ 12,000,000