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Employee Benefit Plans - Additional Information (Detail) - USD ($)
shares in Thousands, $ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2017
Pension Benefits    
Compensation and Retirement Disclosure [Abstract]    
Employer contribution to tax-qualified defined benefit pension plans $ 160 $ 400
RSUs    
Compensation and Retirement Disclosure [Abstract]    
Share-based compensation, other than options, awards granted   1,500
Share-based compensation, vesting period   3 years
Performance Shares    
Compensation and Retirement Disclosure [Abstract]    
Share-based compensation, vesting period   3 years
Share-Based Compensation, vesting date   Dec. 31, 2019
Number of days used to compute performance period average closing price of restricted stock units   20 days
Stock Options    
Compensation and Retirement Disclosure [Abstract]    
Share-based compensation, option awards granted   36
Time Vested Restricted Stock Units RSU    
Compensation and Retirement Disclosure [Abstract]    
Share-based compensation, other than options, awards granted   900
Performance Based Restricted Stock Units RSU    
Compensation and Retirement Disclosure [Abstract]    
Share-based compensation, other than options, awards granted   600