Income Taxes Level 4 (Details) - Components of Income Tax Expense (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Current [Abstract]
Federal	$ 0us-gaap_CurrentFederalTaxExpenseBenefit	$ 0us-gaap_CurrentFederalTaxExpenseBenefit	$ 0us-gaap_CurrentFederalTaxExpenseBenefit
State and local	2	3	(2)
Foreign	26us-gaap_CurrentForeignTaxExpenseBenefit	24us-gaap_CurrentForeignTaxExpenseBenefit	12us-gaap_CurrentForeignTaxExpenseBenefit
Total current	28us-gaap_CurrentIncomeTaxExpenseBenefit	27us-gaap_CurrentIncomeTaxExpenseBenefit	10us-gaap_CurrentIncomeTaxExpenseBenefit
Deferred [Abstract]
Federal	1	332	(365)
State and local	(1)	10	(8)
Foreign	(2)	(20)	(21)
Total deferred	(2)msc_DeferredTaxBenefit	322msc_DeferredTaxBenefit	(394)msc_DeferredTaxBenefit
Income tax expense (benefit)	$ 26us-gaap_IncomeTaxExpenseBenefit	$ 349us-gaap_IncomeTaxExpenseBenefit	$ (384)us-gaap_IncomeTaxExpenseBenefit
Federal Statutory Income Tax Rate	35.00%

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Deferred tax benefit

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Amount of current federal tax expense (benefit) pertaining to income (loss) from continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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