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.

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

Name:	us-gaap_VariableInterestEntityNonconsolidatedCarryingAmountAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Variable Interest Entities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended		9 Months Ended	1 Months Ended	9 Months Ended
	Jul. 31, 2013 CMS 2 [Member]	Sep. 30, 2013 CMS 2 [Member]	Sep. 30, 2013 CMS 2 [Member] NEVADA MW	Sep. 30, 2013 MS 1 [Member]	Sep. 30, 2013 MS 1 [Member] Arizona [Member] MW
Variable Interest Entity [Line Items]
Percentage of variable interests	50.00%			50.00%
Solar energy project			150		150
Solar energy in service			92
Investments including earnings		$ 76		$ 104