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Assumed Health Care Cost Trend Rates Used to Determine Benefit Obligations and Net Cost (Detail) (Postretirement Benefits)
 12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]    
Rate that the cost trend rate is assumed to decline (the ultimate trend rate) 4.50% 5.00%
Year that the rate reaches the ultimate trend rate 2022 2017
Pre Age Sixty Five
    
Defined Benefit Plan Disclosure [Line Items]    
Health care cost trend rate assumed for next year 7.10% [1] 7.50% [1]
Post Age Sixty Five
    
Defined Benefit Plan Disclosure [Line Items]    
Health care cost trend rate assumed for next year 7.50% [1] 7.00% [1]
[1] The pre-65 initial health care cost trend rate is shown first / followed by the post-65 rate.