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Leases and Lease Commitments - Additional Information (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Operating Leased Assets [Line Items]      
Total rental expense $ 1,700 $ 1,700 $ 1,400
Operating lease, asset $ 1,300 $ 1,800  
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List] us-gaap:OtherAssetsMember us-gaap:OtherAssetsMember  
Operating lease, liability $ 1,411 $ 1,800  
Operating lease, weighted average remaining lease term 7 years    
Operating lease, weighted average discount rate, percent 3.20%    
Accounts Payable and Accrued Liabilities      
Operating Leased Assets [Line Items]      
Operating lease, liability $ 494 600  
Other Liabilities      
Operating Leased Assets [Line Items]      
Operating lease, liability 917 $ 1,200  
ASU No. 2016-02      
Operating Leased Assets [Line Items]      
New accounting pronouncement or change in accounting principle effect of additional assets and liabilities $ 1,300