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Employee Benefit Plans (Accumulated Benefit Obligation in Excess of Plan Assets) (Detail) - USD ($)
$ in Millions
Dec. 31, 2019
Dec. 31, 2018
General Discussion Of Pension And Other Postretirement Benefits [Abstract]    
Accumulated benefit obligation $ 8,852 $ 7,056
Fair value of plan assets $ 7,471 $ 5,398