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Employee Benefits - Narrative (Detail)
$ in Millions
 12 Months Ended
Dec. 31, 2023
USD ($)
plan
shares
Dec. 31, 2022
USD ($)
Dec. 31, 2021
USD ($)
Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]        
Accumulated benefit obligation for all defined benefit pension plans $ 15,100 $ 15,300    
Defined benefit plan, benefit obligation, actuarial gain (loss) from healthcare cost assumptions used calculating benefit obligation, discount rate $ (534)      
Weighted-average healthcare cost trend rate assumed for next year 7.30% 6.60% 6.20%  
Defined benefit plan, benefit obligation, actuarial gain (loss) from assumptions used calculating benefit obligation, discount rate $ (503) $ 7,000 $ 1,100  
Discount Rate 5.00% 5.20% 2.90% 2.60%
Defined benefit plan, reclassification adjustment from AOCI $ 252 $ 390 $ 708  
Defined benefit plan, period used to determine overall expected long term rate of return on assets assumption (in years) 10 years      
Number of leveraged employee stock ownership plans (ESOP) | plan 4      
Number of allocated shares of common stock in ESOP (in shares) | shares 42,000,000      
Number of unallocated shares of common stock in ESOP (in shares) | shares 0      
Total savings plan cost $ 724 620 690  
Defined benefit plan, actuarial gain (loss), immediate recognition as component in net periodic benefit (cost) credit (992) 1,700 2,400  
Pension and benefit credits (charges) from actual return   (5,500) 847  
Defined benefit plan, benefit obligation, actuarial gain (loss) from actuarial assumption adjustments 45 206 453  
Severance liability charged to expense 531 319 233  
Minimum        
Defined Benefit Plan Disclosure [Line Items]        
Selected bonds $ 300      
Minimum | Return Seeking Assets        
Defined Benefit Plan Disclosure [Line Items]        
Target allocation percentage of assets 34.00%      
Minimum | Liability Hedging Assets        
Defined Benefit Plan Disclosure [Line Items]        
Target allocation percentage of assets 62.00%      
Maximum | Return Seeking Assets        
Defined Benefit Plan Disclosure [Line Items]        
Target allocation percentage of assets 44.00%      
Maximum | Liability Hedging Assets        
Defined Benefit Plan Disclosure [Line Items]        
Target allocation percentage of assets 72.00%      
Maximum | Cash and cash equivalents        
Defined Benefit Plan Disclosure [Line Items]        
Target allocation percentage of assets 10.00%      
Pension        
Defined Benefit Plan Disclosure [Line Items]        
Defined benefit plan, benefit obligation, actuarial gain (loss) from assumptions used calculating benefit obligation, discount rate $ (288) $ 4,100    
Discount Rate 5.00% 5.20%    
Company contributions $ 252 $ 53    
Defined benefit plan, actuarial gain (loss), immediate recognition as component in net periodic benefit (cost) credit (266) (1,505) 1,419  
Pension | Qualified Plan        
Defined Benefit Plan Disclosure [Line Items]        
Company contributions 200      
Pension | Nonqualified Plan        
Defined Benefit Plan Disclosure [Line Items]        
Company contributions 52      
Health Care and Life        
Defined Benefit Plan Disclosure [Line Items]        
Defined benefit plan, benefit obligation, actuarial gain (loss) from assumptions used calculating benefit obligation, discount rate $ (215) $ 2,900    
Discount Rate 5.00% 5.20%    
Company contributions $ 936 $ 692    
Defined benefit plan contributions by employer in next fiscal year 770      
Defined benefit plan, actuarial gain (loss), immediate recognition as component in net periodic benefit (cost) credit $ (726) $ 3,182 $ 960  
Pension and Postretirement Plan        
Defined Benefit Plan Disclosure [Line Items]        
Discount Rate 5.00%