Commitments and Contingencies - Commitments (Details) (USD $)	Sep. 30, 2013 Solar Star Funding [Member]	Aug. 31, 2013 Public utilities, inventory, fuel, contract extension [Member] PacifiCorp [Member]	Sep. 30, 2013 Wind-powered generating facilities [Member] MidAmerican Funding [Member] MWs	Jul. 31, 2013 Multi-value projects [Member] MidAmerican Funding [Member]	Jun. 30, 2013 Solar Star Funding [Member] Solar Star Funding, LLC series A senior secured notes, 5.375%, due June 2016 through June 2035 [Member] Subsidiary Debt [Member]
ContractualObligationFiscalYearMaturityScheduleTable [Line Items]
Debt instrument, face amount					$ 1,000,000,000
Debt instrument, interest rate, stated percentage					5.375%
Equity funding and contribution agreement, amount committed	2,750,000,000
Equity commitment, outstanding amount	1,750,000,000
Megawatt nominal ratings			1,050
Purchase obligation			1,300,000,000	342,000,000
Purchase obligation, due in next twelve months			343,000,000	17,000,000
Purchase obligation, due in second year			522,000,000	140,000,000
Purchase obligation, due in third year			447,000,000	149,000,000
Purchase obligation, due in fourth year		95,000,000		36,000,000
Purchase obligation, due in fifth year		96,000,000
Purchase obligation, due after fifth year		$ 298,000,000