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Employee Benefit Plans - Additional Information (Detail)
$ in Millions
9 Months Ended
Sep. 30, 2017
USD ($)
Defined Benefit Plan Disclosure [Line Items]  
Expected additional cash contributions $ 6
Defined benefit pension plans  
Defined Benefit Plan Disclosure [Line Items]  
Cash contributions made during the period 3
Postretirement benefit plans  
Defined Benefit Plan Disclosure [Line Items]  
Cash contributions made during the period $ 1