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Pension and Other Postretirement Benefits - Schedule of Assumed Health Care Cost Trend Rates (Detail)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Defined Benefit Plan Disclosure [Line Items]      
Health care cost trend rate assumed for next year 6.00% 6.50% 6.50%
Rate to which the cost trend rate gradually declines 4.50% 5.00% 5.00%
Year that the rate reaches the rate at which it is assumed to remain 2017 2016 2015