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Pension Plans, Other Postretirement Benefits, and Defined-Contribution Plans - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Compensation and Retirement Disclosure [Abstract]      
Defined-benefit plan, amortization of net actuarial loss in 2016 $ 34,000,000    
Defined benefit plan, amortization of prior service credit in 2016 $ 27,000,000    
Defined benefit plan, annual rate of increase assumed for next fiscal year 1.75%    
Defined-benefit plan, health care cost trend rate assumed for next fiscal year   8.00%  
Defined Benefit Plan Disclosure [Line Items]      
Defined benefit plan, amount of employer securities included in plan assets $ 0    
Defined-contribution plans, recognized expense $ 76,000,000 $ 76,000,000 $ 78,000,000
Equity Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined-benefit plan, target asset-allocation range, minimum 45.00%    
Defined-benefit plan, target asset-allocation range, maximum 55.00%    
Fixed Income [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined-benefit plan, target asset-allocation range, minimum 20.00%    
Defined-benefit plan, target asset-allocation range, maximum 30.00%    
Other Investments [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined-benefit plan, target asset-allocation range, maximum 25.00%