Employee Benefit and Retirement Plans - Schedule of Reconciliation of Benefit Obligations (Parenthetical) (Detail) - USD ($) $ in Billions	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan [Abstract]
Accumulated benefit obligation	$ 2.3	$ 2.2

Amount of actuarial present value of benefits attributed to employee service rendered, excluding assumptions about future compensation level.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

Name:	us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant