Guarantees (Details) (USD $) In Millions, unless otherwise specified			12 Months Ended
Dec. 31, 2012 NORESCO Guarantees, Total	Dec. 31, 2008 NORESCO Guarantees, Total	Dec. 31, 2012 NORESCO Guarantees, Energy Savings
Undiscounted maximum aggregate payments related to guarantees			$ 192
Guarantee obligations term			P15Y
NORESCO purchaser's obligation for loss reimbursement to the company, maximum exposure	6
Third party letter of credit amount supporting the NORESCO purchaser's guarantee obligations		$ 1

Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

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

-Publisher FASB

-Name FASB Interpretation (FIN)

-Number 45

-Paragraph 13

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 460

-SubTopic 10

-Section 50

-Paragraph 4

-Subparagraph (b)(1)

-URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12069-110248

Name:	us-gaap_GuaranteeObligationsMaximumExposure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant