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Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013 | Jul. 04, 2013
Schedule of Regulatory Assets and Liabilities [Line Items] |  |  |  |  |
Total Current Regulatory Assets |  | $ 746 | $ 637 |  |
Total Non Current Regulatory Assets |  | 918 | 872 |  |
TOTAL REGULATORY ASSETS |  | 1,664 | 1,509 |  |
Total Current Regulatory Liabilities |  | 465 | 605 |  |
Total Non Current Regulatory Liabilities |  | $ 1,286 | $ 1,509 |  |
Total period for adjustments to the Regulatory Asset Base (Up to) |  | 4 years | 4 years |  |
TOTAL REGULATORY LIABILITIES |  | $ 1,751 | $ 2,114 | $ 269 |
Period of annual tariff adjustment |  | 12 months |  |  |
Total period to recover or refund costs for annual tariff adjustment |  | 24 months |  |  |
Brazil Tariff Estimated Rate Change Liability |  |  |  |  |
Schedule of Regulatory Assets and Liabilities [Line Items] |  |  |  |  |
Total Current Regulatory Liabilities | [1] | $ 0 | $ 76 |  |
Total period to recover or refund costs for annual tariff adjustment |  |  | 2 years |  |
Tariff adjustment, percentage amortized |  |  |  |  | 67.55%
Tariff adjustment, percentage amortized in next tariff adjustment |  |  |  |  | 32.45%
Efficiency Program Costs |  |  |  |  |
Schedule of Regulatory Assets and Liabilities [Line Items] |  |  |  |  |
Total Current Regulatory Liabilities | [2] | 12 | $ 22 |  |
Total Non Current Regulatory Liabilities | [2] | 5 | 11 |  |
Brazil Regulatory Asset Base Adjustment |  |  |  |  |
Schedule of Regulatory Assets and Liabilities [Line Items] |  |  |  |  |
Total Current Regulatory Liabilities | [3] | 169 | 123 |  |
Total Non Current Regulatory Liabilities | [3] | 86 | 61 |  |
Brazil Tariff Recoveries Energy Purchases Liability |  |  |  |  |
Schedule of Regulatory Assets and Liabilities [Line Items] |  |  |  |  |
Total Current Regulatory Liabilities | [4] | 105 | 144 |  |
Total Non Current Regulatory Liabilities | [4] | 30 | 128 |  |
Brazil Tariff Recoveries Transmission Costs Regulatory Fees And Other Liability |  |  |  |  |
Schedule of Regulatory Assets and Liabilities [Line Items] |  |  |  |  |
Total Current Regulatory Liabilities | [4] | 120 | 174 |  |
Total Non Current Regulatory Liabilities | [4] | 29 | 97 |  |
Asset Retirement Obligation Costs |  |  |  |  |
Schedule of Regulatory Assets and Liabilities [Line Items] |  |  |  |  |
Total Non Current Regulatory Liabilities | [5] | 759 | 727 |  |
Brazil Special Obligations |  |  |  |  |
Schedule of Regulatory Assets and Liabilities [Line Items] |  |  |  |  |
Total Non Current Regulatory Liabilities | [6] | 370 | 484 |  |
Other Regulatory Liabilities |  |  |  |  |
Schedule of Regulatory Assets and Liabilities [Line Items] |  |  |  |  |
Total Current Regulatory Liabilities | [7] | 59 | 66 |  |
Total Non Current Regulatory Liabilities | [7] | 7 | 1 |  |
Brazil Tariff Recoveries Energy Purchases Asset |  |  |  |  |
Schedule of Regulatory Assets and Liabilities [Line Items] |  |  |  |  |
Total Current Regulatory Assets | [4] | 416 | 424 |  |
Total Non Current Regulatory Assets | [4] | 147 | 266 |  |
Brazil Tariff Recoveries Transmission Costs Regulatory Fees And Other Asset |  |  |  |  |
Schedule of Regulatory Assets and Liabilities [Line Items] |  |  |  |  |
Total Current Regulatory Assets | [4] | 264 | 63 |  |
Total Non Current Regulatory Assets | [4] | 140 | 14 |  |
El Salvador Tariff Recoveries |  |  |  |  |
Schedule of Regulatory Assets and Liabilities [Line Items] |  |  |  |  |
Total Current Regulatory Assets | [8] | 43 | 92 |  |
Pension Costs |  |  |  |  |
Schedule of Regulatory Assets and Liabilities [Line Items] |  |  |  |  |
Total Non Current Regulatory Assets | [9],[10] | 227 | 329 |  |
Income Taxes Recoverable From Customers |  |  |  |  |
Schedule of Regulatory Assets and Liabilities [Line Items] |  |  |  |  |
Total Non Current Regulatory Assets | [9],[11] | 36 | 74 |  |
Deferred Midwest Independent Service Operator Costs |  |  |  |  |
Schedule of Regulatory Assets and Liabilities [Line Items] |  |  |  |  |
Total Non Current Regulatory Assets | [12] | 129 | 111 |  |
Other Regulatory Assets |  |  |  |  |
Schedule of Regulatory Assets and Liabilities [Line Items] |  |  |  |  |
Total Current Regulatory Assets | [13] | 23 | 58 |  |
Total Non Current Regulatory Assets | [13] | 239 | 78 |  |
Other current regulatory assets that did not earn a rate of return |  | 8 | 22 |  |
Other noncurrent regulatory assets that did not earn a rate of return |  | $ 237 | $ 73 |  |
[1] | (8)In July 2012, the Brazilian energy regulator (the "Regulator") approved the periodic review and reset of a component of Eletropaulo's regulated tariff, which determines the margin to be earned by Eletropaulo. The review and reset of this tariff component was retroactive to July 2011 and applied to customers' invoices from July 2012 to June 2015. From July 2011 through June 2012, Eletropaulo invoiced customers under the then-existing tariff rate, as required by the Regulator. As the new tariff rate was lower than the previous rate, Eletropaulo was required to reduce customer tariffs for the difference over the next year. Accordingly, from July 2011 through June 2012, Eletropaulo recognized a regulatory liability for the estimated future refunds, subsequently adjusted as of June 30, 2012 upon the finalization of the new tariff with the Regulator. The refund to customers was considered in the 2013 tariff adjustment, which contemplated an amortization of 67.55% from July 4, 2013. The remaining balance, representing 32.45%, was considered in the next annual tariff adjustment. There was no recorded current regulatory liability at Eletropaulo as of December 31, 2015.
[2] | (9)Amounts received for costs expected to be incurred to improve the efficiency of our plants in Brazil as part of the IRT.
[3] | (13) Represents adjustments to the RAB resulting from an administrative ruling in December 2013 compelling Eletropaulo to refund customers beginning July 2014.
[4] | (1)Recoverable or refundable per Brazilian National Electric Energy Agency ("ANEEL") regulations through the Annual Tariff Adjustment ("IRT"). These costs are generally non-controllable and primarily consist of purchased electricity, energy transmission, and sector costs that are considered volatile. The costs are passed through for a period of 12 months as part of the IRT. Any remaining balance is considered in the subsequent IRT, which results in a total of 24 months to recover or refund the costs. Favorable spot market sales are also subject to customer refunds through the IRT over the course of these time periods.
[5] | (11)Obligations for removal costs which do not have an associated legal retirement obligation as defined by the accounting standards on asset retirement obligations.
[6] | (12)Obligations established by ANEEL in Brazil associated with electric utility concessions and represent amounts received from customers or donations not subject to return. These donations are allocated to support energy network expansion and to improve utility operations to meet customers' needs. The term of the obligation is established by ANEEL. Settlement shall occur when the concession ends.
[7] | (10)Other current and noncurrent regulatory liabilities primarily consist of liabilities owed to electricity generators due to variance in energy prices during rationing periods ("Free Energy"). Our Brazilian subsidiaries are authorized to refund this cost associated with monthly energy price variances between the wholesale energy market prices owed to the power generation plants producing Free Energy and the capped price reimbursed by the local distribution companies which are passed through to the final customers through energy tariffs. The balance excludes asset retirement obligations that were reclassified out of Other.
[8] | (2)Deferred fuel costs incurred by our El Salvador subsidiaries associated with purchase of energy from the El Salvador spot market and power generation plants. In El Salvador, the deferred fuel adjustment represents the variance between the actual fuel costs and the fuel costs recovered in the tariffs. The variance is recovered quarterly in the tariff reset period.
[9] | (4)Past expenditures on which the Company does not earn a rate of return.
[10] | (5)The regulatory accounting standards allow the defined pension and postretirement benefit obligation to be recorded as a regulatory asset equal to the previously unrecognized actuarial gains and losses and prior service costs that are expected to be recovered through future rates. Pension expense is recognized based on the plan's actuarially determined pension liability. Recovery of costs is probable, but not yet determined. Pension contributions made by our Brazilian subsidiaries are not included in regulatory assets as those contributions are not covered by the established tariff in Brazil.
[11] | (6)Probable recovery through future rates, based upon established regulatory practices, which permit the recovery of current taxes. This amount is expected to be recovered, without interest, over the period as book-tax temporary differences reverse and become current taxes.
[12] | (7)Transmission service costs and other administrative costs from IPL's participation in the Midwest ISO market, which are recoverable but do not earn a rate of return. Recovery of costs is probable, but the timing is not yet determined.
[13] | (3)Includes assets with and without a rate of return. Other current regulatory assets that did not earn a rate of return were $8 million and $22 million, as of December 31, 2015 and 2014, respectively. Other noncurrent regulatory assets that did not earn a rate of return were $237 million and $73 million, as of December 31, 2015 and 2014, respectively. Other current and noncurrent regulatory assets primarily consist of:▪Unamortized losses on long-term debt reacquired or redeemed in prior periods at IPL and DPL, which are amortized over the lives of the original issues in accordance with the Federal Energy Regulatory Commission ("FERC") and PUCO rules.▪Unamortized carrying charges and certain other costs related to Petersburg unit 4 at IPL.▪Deferred storm costs incurred primarily in 2008 to repair storm damage at DPL; recovery was approved via order from the PUCO on December 17, 2014 and began January 2015.▪Additional Regulatory Asset Base ("RAB") from a favorable decision on tariff reset (administrative appeal) at Eletropaulo.

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- Definition Remaining balance of current regulatory assets for which no return on investment during recovery is provided. In some cases, a regulator may permit an enterprise to include a cost that would be charged to expense by an unregulated enterprise as an allowable cost over a period of time by amortizing that cost for rate-making purposes, but the regulator does not include the unrecovered amount in the rate base. + References No definition available. + Details
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- Definition Remaining balance of noncurrent regulatory assets for which no return on investment during recovery is provided. In some cases, a regulator may permit an enterprise to include a cost that would be charged to expense by an unregulated enterprise as an allowable cost over a period of time by amortizing that cost for rate-making purposes, but the regulator does not include the unrecovered amount in the rate base + References No definition available. + Details
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- Definition The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382 + Details
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- Definition Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382 + Details
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