Changes in Balance of Accumulated Other Comprehensive Loss (Parenthetical) (Detail) - USD ($) $ in Billions	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Post retirement benefit plan adjustments, tax benefits	$ 6.2	$ 6.4	$ 5.3

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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