Recently Issued Accounting Standards - Additional Information (Detail)	Aug. 31, 2018
New Accounting Guidance Issued and Not Yet Adopted
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Defined benefit plan effect of percentage change in assumed health care cost trend rates	1.00%

Ultimate trend rate for health care cost for defined benefit postretirement plan.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (l)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

Name:	us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant