Variable Interest Entities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended	12 Months Ended
Aug. 31, 2011	Dec. 31, 2013 VIE
Variable Interest Entity [Line Items]
Number of VIEs, long-term electricity purchase agreements		5
Solar energy project cost		$ 90
Operation commenced date	Aug. 01, 2011
Assets related to Pilesgrove		25
Additional financing obligation		25
CMS 2 [Member]
Variable Interest Entity [Line Items]
Assets related to Pilesgrove		75
Percentage of variable interests		50.00%
CMS 2 [Member] \| Nevada [Member]
Variable Interest Entity [Line Items]
Solar energy project		150
Solar energy in service		92
MS 1 [Member]
Variable Interest Entity [Line Items]
Assets related to Pilesgrove		$ 104
Percentage of variable interests		50.00%
MS 1 [Member] \| Arizona [Member]
Variable Interest Entity [Line Items]
Solar energy project		150

Generating Capacity

No definition available.

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- Definition

Number Of Variable Interest Entities

+ References

No definition available.

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- Definition

Solar Energy In Service

+ References

No definition available.

+ Details

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- Definition

Cost incurred in providing energy services during the reporting period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.2(d))

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

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- Definition

Date the operations of the entity commenced, in CCYY-MM-DD format.

+ References

No definition available.

+ Details

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- Details

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- Definition

Carrying amount of the assets in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the Variable Interest Entity (VIE), where the reporting entity is not the VIE's primary beneficiary.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 810

-SubTopic 10

-Section 50

-Paragraph 4

-Subparagraph a

-URI http://asc.fasb.org/extlink&oid=28200181&loc=d3e5728-111685

+ Details

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- Definition

Carrying amount of the liabilities in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the Variable Interest Entity (VIE), where the reporting entity is not the VIE's primary beneficiary.

+ References

+ Details

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- Definition

Percentage of the Variable Interest Entity's (VIE) voting interest owned by (or beneficial interest in) the reporting entity (directly or indirectly).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 810

-SubTopic 10

-Section 50

-Paragraph 5A

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=28200181&loc=SL6759159-111685

+ Details

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