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OTHER FINANCIAL DATA - U.S. TREASURY GRANT RECEIVABLE (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 12 Months Ended
Mar. 31, 2013
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
U.S. Treasury Grants Receivable [Line Items]        
Proceeds from U.S. Treasury grants   $ 0sre_ProceedsFromUsTreasuryGrants $ 238sre_ProceedsFromUsTreasuryGrants $ 0sre_ProceedsFromUsTreasuryGrants
Reduction in tax benefit due to sequestration 5sre_ReductionInTaxBenefitDueToSequestration      
Sequestration of U.S. Treasury grants receivable   $ 0sre_SequestrationOfUsTreasuryGrantsReceivable $ 23sre_SequestrationOfUsTreasuryGrantsReceivable $ 0sre_SequestrationOfUsTreasuryGrantsReceivable