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Employee Benefit Plans (Benefit Obligation in Excess of Plan Assets) (Detail) - USD ($)
$ in Millions
Dec. 31, 2021
Dec. 31, 2020
Pension Benefits    
Defined Benefit Plan Disclosure [Line Items]    
Benefit obligation $ 9,420 $ 10,697
Fair value of plan assets 9,229 9,259
Other Postretirement Benefits    
Defined Benefit Plan Disclosure [Line Items]    
Benefit obligation 261 305
Fair value of plan assets $ 7 $ 9