Summarized Financial Information of Unconsolidated Affiliate Level 4 (Details) - HAI Balance Sheets (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
HAI Summarized Financial Information [Line Items]
Current Assets	$ 37	$ 35
Non-current assets	12	13
Current Liabilities	22	21
Non-current liabilities	$ 0	$ 0

Non-current Liabilities of Unconsolidated Affiliate

No definition available.

Name:	msc_NonCurrentLiabilitiesOfUnconsolidatedAffiliate
Namespace Prefix:	msc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant