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Pension and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Detail) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Defined Benefit Plan Disclosure [Line Items]    
Net periodic benefit cost $ 54 $ 83
Net periodic benefit costs continuing and discontinued    
Net periodic benefit cost 54 83
Pension Benefits [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Service cost 23 40
Interest cost 58 122
Expected return on plan assets (83) (185)
Recognized net actuarial loss 55 102
Amortization of prior service cost (benefits) 1 4
Special termination benefits   1
Net periodic benefit cost 54 84
Net periodic benefit costs continuing and discontinued    
Discontinued operations   33
Net amount recognized in Statement of Consolidated Operations 54 51
Net periodic benefit cost 54 84
Other Postretirement Benefits [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Service cost 2 3
Interest cost 8 18
Recognized net actuarial loss 1 6
Amortization of prior service cost (benefits) (2) (6)
Net periodic benefit cost 9 21
Net periodic benefit costs continuing and discontinued    
Discontinued operations   12
Net amount recognized in Statement of Consolidated Operations 9 9
Net periodic benefit cost $ 9 $ 21