Changes In Fair Value of Level 3 Financial Assets (Detail) (USD $)	3 Months Ended	9 Months Ended
Sep. 30, 2011	Sep. 30, 2011
Balance, beginning of the period	$ 99,154,000	$ 146,044,000
Calls at par value	(13,100,000)	(64,600,000)
Decrease in previously recognized unrealized losses included in other comprehensive income	(4,963,000)	(353,000)
Balance, end of the period	$ 81,091,000	$ 81,091,000

Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Calls, At Par

Name:	emc_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetCallsAtPar
Namespace Prefix:	emc
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This element represents total gains or losses for the period (realized and unrealized), arising from assets measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in other comprehensive income (a separate component of shareholders' equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph c(1)

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncome
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This element represents an asset measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph c

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant