XML 28 R39.htm IDEA: XBRL DOCUMENT v2.4.0.6

Summary of significant accounting policies (Details 2)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Depreciation
Composite annual depreciation rate (as a percent)	3.20%	3.50%	3.80%
Minimum
Depreciation
Estimated useful life under production plant (in years)	20 years
Estimated useful life under transmission and distribution plant (in years)	25 years
Estimated useful life under general plant (in years)	5 years
Maximum
Depreciation
Estimated useful life under production plant (in years)	88 years
Estimated useful life under transmission and distribution plant (in years)	65 years
Estimated useful life under general plant (in years)	50 years

X

- Definition

Estimated useful life of property, plant and equipment (PPE) related to assets common to business units owned by public utility.

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilitiesPropertyPlantAndEquipmentCommonEstimatedUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Discloses the overall composite depreciation rate for pubic utility plants in service for each year an income statement is presented.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 360

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 10.C)

-URI http://asc.fasb.org/extlink&oid=6500719&loc=d3e659983-123033



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.13(a))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Estimated useful life of property, plant and equipment (PPE) related to utility generation owned by the public utility.

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilitiesPropertyPlantAndEquipmentGenerationEstimatedUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Estimated useful life of property, plant and equipment (PPE) related to utility transmission and distribution owned by public utility.

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilitiesPropertyPlantAndEquipmentTransmissionAndDistributionEstimatedUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_PublicUtilityPropertyPlantAndEquipmentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration