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Employee Benefits - Estimated Benefits Expected to be Paid (Detail) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2012
Pension Benefits [Member]
Dec. 31, 2011
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]    
2013 $ 93 $ 14
2014 101 15
2015 136 17
2016 114 18
2017 123 20
2018-2022 $ 771 $ 124