Related Party Information - Additional Information (Detail) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2017	Dec. 31, 2016
EXOR N.V [Member]
Related Party Transaction [Line Items]
Percentage of common shares outstanding held by related parties	41.70%
IVECO-OTO MELARA Societa Consortile [Member]
Related Party Transaction [Line Items]
Pledged guarantees on commitments	$ 267	$ 187

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