Pension and Other Benefit Programs - Estimated Future Benefit Payments (Parenthetical) (Detail) $ in Millions	Sep. 30, 2017 USD ($)
Postretirement Medical Plans
Defined Benefit Plan Disclosure [Line Items]
Expected Medicare subsidy receipts	$ 79

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.

Name:	us-gaap_DefinedBenefitPlanDisclosureLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration