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Employee Benefit Plans - Additional Information (Detail) - USD ($)
shares in Millions, $ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2018
Compensation and Retirement Disclosure [Abstract]    
Number of days used to compute performance period average closing price of restricted stock units   20 days
Pension Benefits    
Compensation and Retirement Disclosure [Abstract]    
Employer contribution to tax-qualified defined benefit pension plans $ 47 $ 160
RSUs    
Compensation and Retirement Disclosure [Abstract]    
Share-based compensation, option awards granted   1.8
Share-based compensation, vesting period   3 years
Time Vested Restricted Stock Units RSU    
Compensation and Retirement Disclosure [Abstract]    
Share-based compensation, other than options, awards granted   1.1
Performance Based Restricted Stock Units RSU    
Compensation and Retirement Disclosure [Abstract]    
Share-based compensation, other than options, awards granted   0.7