Recently Issued Accounting Standards - Additional Information (Detail) - Recently Issued Accounting Standards $ in Millions	Sep. 30, 2016 USD ($)
Pension Benefits
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Pension plan investments measured at net asset value per share	$ 1,900
Short-term Investments
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Investments in certain entities that calculate net asset value per share included in short-term investments	$ 202

Fair value of investments in certain entities that calculate net asset value per share, including, but not limited to, by unit, membership interest, or other ownership interest. Investments include, but are not limited to, investments in certain hedge funds, venture capital funds, private equity funds, real estate partnerships or funds.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 6A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=SL6742756-110258

Name:	us-gaap_AlternativeInvestmentsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant