Pension and Other Postretirement Benefits - Additional Information (Detail) $ in Millions	3 Months Ended
Mar. 31, 2016 USD ($)
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Change in interest cost component of net periodic benefit cost determination	$ 24
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Change in interest cost component of net periodic benefit cost determination	$ 4

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