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Postretirement Benefit Plans - Summary of Estimated Future Pension Benefit Payments (Detail) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2012
Defined Benefit Plan, Expected Future Benefit Payments [Line Items]  
2013 $ 16
2014 13
2015 15
2016 14
2017 14
Years 2018-2022 $ 95