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Intangible Assets - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Goodwill And Intangible Assets Disclosure [Abstract]    
Amortization expense $ 165 $ 169
Estimated amortization charged to income, remaining three quarters of 2018 519  
Estimated amortization charged to income, 2019 672  
Estimated amortization charged to income, 2020 640  
Estimated amortization charged to income, 2021 617  
Estimated amortization charged to income, 2022 607  
Estimated amortization charged to income, 2023 $ 594