Pension and Other Postretirement Benefits - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2016	Jun. 30, 2016
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Change in interest cost component of net periodic benefit cost determination	$ 24	$ 48
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Change in interest cost component of net periodic benefit cost determination	$ 4	$ 8

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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