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Summary of Significant Accounting Policies
12 Months Ended
Dec. 31, 2012
Summary of Significant Accounting Policies [Abstract]  
Basis of Presentation and Significant Accounting Policies [Text Block]
Summary of Significant Accounting Policies
 
Basis of Presentation
 
General
Our accounting records are maintained in United States dollars, and all references to dollars are United States dollars, except where stated otherwise.  Canadian dollars are designated as C$.
 
Our accompanying consolidated financial statements include our accounts and those of our operating partnerships and their majority-owned and controlled subsidiaries, and we have prepared these consolidated financial statements under the rules and regulations of the United States Securities and Exchange Commission.  These rules and regulations conform to the accounting principles contained in the Financial Accounting Standards Board’s Accounting Standards Codification, the single source of generally accepted accounting principles in the United States of America.  Under such rules and regulations, all significant intercompany items have been eliminated in consolidation.  Additionally, certain amounts from prior years have been reclassified to conform to the current presentation.  In this report, we refer to the Financial Accounting Standards Board as the FASB and the FASB Accounting Standards Codification as the Codification.

Our financial statements are consolidated into the consolidated financial statements of KMI; however, except for the related party transactions described in Note 11 “Related Party Transactions—Asset Acquisitions and Sales,” KMI is not liable for, and its assets are not available to satisfy, the obligations of us and/or our subsidiaries and vice versa.  Responsibility for payments of obligations reflected in our or KMI’s financial statements is a legal determination based on the entity that incurs the liability.  Furthermore, the determination of responsibility for payment among entities in our consolidated group of subsidiaries is not impacted by the consolidation of our financial statements into the consolidated financial statements of KMI.
FTC Natural Gas Pipelines Disposal Group – Discontinued Operations
Effective November 1, 2012, KMI sold our (i) Kinder Morgan Interstate Gas Transmission natural gas pipeline system; (ii) Trailblazer natural gas pipeline system; (iii) Casper and Douglas natural gas processing operations; and (iv) 50% equity investment in the Rockies Express natural gas pipeline system to Tallgrass Energy Partners, LP for approximately $1.8 billion in cash. In this report, we refer to this combined group of assets as our FTC Natural Gas Pipelines disposal group. The sale of our FTC Natural Gas Pipelines disposal group satisfied terms of a March 15, 2012 agreement between KMI and the U.S. Federal Trade Commission (FTC) to divest certain of our assets in order to receive regulatory approval for KMI’s EP acquisition.
Following KMI’s agreement with the FTC, we accounted for our FTC Natural Gas Pipelines disposal group as discontinued operations in accordance with the provisions of the “Presentation of Financial Statements—Discontinued Operations” Topic of the Codification. Accordingly, we (i) reclassified and excluded the FTC Natural Gas Pipelines disposal group’s results of operations from our results of continuing operations and reported the disposal group’s results of operations separately as “Income from operations of FTC Natural Gas Pipelines disposal group” within the discontinued operations section of our accompanying consolidated statements of income for all periods presented; and (ii) separately reported a “(Loss) on remeasurement to fair value and sale of FTC Natural Gas Pipelines disposal group” within the discontinued operations section of our accompanying consolidated statements of income for the year ended December 31, 2012. We did not, however, elect to present separately the operating, investing and financing cash flows related to the disposal group in our accompanying consolidated statements of cash flows.
For more information about the divestiture of our FTC Natural Gas Pipelines disposal group, see Note 3 “Acquisitions and Divestitures—Divestitures—FTC Natural Gas Pipelines Disposal Group - Discontinued Operations.”
August 2012 KMI Asset Drop-Down    
Effective August 1, 2012, we acquired the full ownership interest in the Tennessee Gas natural gas pipeline system and a 50% ownership interest in the El Paso Natural Gas pipeline system from KMI for an aggregate consideration of approximately $6.2 billion. In this report, we refer to this acquisition of assets from KMI as the drop-down transaction; the combined group of assets acquired from KMI as the drop-down asset group; the Tennessee Gas natural gas pipeline system or Tennessee Gas Pipeline Company, L.L.C. as TGP, and the El Paso Natural Gas pipeline system or El Paso Natural Gas Pipeline Company, L.L.C. as EPNG.
KMI acquired the drop-down asset group as part of its acquisition of EP on May 25, 2012 (discussed above in Note 1). Pursuant to current accounting principles in conformity with the Codification, KMI accounted for its acquisition of the drop-down asset group under the purchase accounting method, and we accounted for the drop-down transaction as a transfer of net assets between entities under common control. Accordingly, we prepared our consolidated financial statements and the related financial information contained in this report to reflect the transfer of net assets from KMI to us as if such transfer had taken place on May 25, 2012. Specifically, we (i) recognized the acquired assets and assumed liabilities at KMI’s carrying value as of its acquisition date, May 25, 2012 (including all of KMI’s purchase accounting adjustments); (ii) recognized any difference between our purchase price and the carrying value of the net assets we acquired as an adjustment to our Partners’ Capital (specifically, as an adjustment to our general partner’s capital interests); and (iii) retrospectively adjusted our consolidated financial statements, for any date after KMI’s May 25, 2012 acquisition of EP, to reflect our results on a consolidated combined basis including the results of the drop-down asset group as of or at the beginning of the respective period.
Additionally, because KMI both controls us and consolidates our financial statements into its consolidated financial statements as a result of its ownership of our general partner, we fully allocated to our general partner:
the earnings of the drop-down asset group for the period beginning May 25, 2012 and ending August 1, 2012 (and we reported this amount separately as “Pre-acquisition income from operations of drop-down asset group allocated to General Partner“ within the Calculation of Limited Partners’ Interest in Net Loss section of our accompanying consolidated statements of income for the year ended December 31, 2012); and
incremental severance expense related to KMI’s acquisition of EP and allocated to us from KMI (and we reported this amount separately as “Drop-down asset group severance expense allocated to General Partner” within the Calculation of Limited Partners’ Interest in Net Loss section of our accompanying consolidated statements of income for the year ended December 31, 2012. We do not have any obligation, nor did we pay any amounts related to this expense.
We allocated all other 2012 earnings amounts to all of our partners according to the partnership agreements. For more information about the drop-down transaction, see Note 3 “Acquisitions and Divestitures—August 2012 KMI Asset Drop-Down.” For more information on the changes to our Partners’ Capital related to the drop-down transaction, see Note 10 “Partners’ Capital—Adjustment to Partners’ Capital from August 2012 KMI Asset Drop-Down.”
Use of Estimates
 
Certain amounts included in or affecting our financial statements and related disclosures must be estimated, requiring us to make certain assumptions with respect to values or conditions which cannot be known with certainty at the time our financial statements are prepared.  These estimates and assumptions affect the amounts we report for assets and liabilities, our revenues and expenses during the reporting period, and our disclosure of contingent assets and liabilities at the date of our financial statements.  We evaluate these estimates on an ongoing basis, utilizing historical experience, consultation with experts and other methods we consider reasonable in the particular circumstances.  Nevertheless, actual results may differ significantly from our estimates.  Any effects on our business, financial position or results of operations resulting from revisions to these estimates are recorded in the period in which the facts that give rise to the revision become known.
 
In addition, we believe that certain accounting policies are of more significance in our financial statement preparation process than others, and set out below are the principal accounting policies we apply in the preparation of our consolidated financial statements.
 
Cash Equivalents and Restricted Deposits
 
We define cash equivalents as all highly liquid short-term investments with original maturities of three months or less.

Cash held in escrow is restricted cash, and as of December 31, 2012, our restricted cash consisted of (i) $2 million deposited into a third-party escrow account to comply with certain contractual stipulations related to our Canadian terminal operations; and (ii) $5 million consisting of cash margin deposits associated with our energy commodity contract positions and over-the-counter swap partners. We reported this combined $7 million amount within “Other current assets” on our accompanying consolidated balance sheet.  As of December 31, 2011, none of our cash was set aside or restricted for some special purpose.  
 
Accounts Receivable
 
The amounts reported as “Accounts, notes and interest receivable, net” on our accompanying consolidated balance sheets as of December 31, 2012 and 2011 primarily consist of amounts due from third party payors (unrelated entities).  For information on receivables due to us from related parties, see Note 11.
 
Our policy for determining an appropriate allowance for doubtful accounts varies according to the type of business being conducted and the customers being served.  Generally, we make periodic reviews and evaluations of the appropriateness of the allowance for doubtful accounts based on a historical analysis of uncollected amounts, and we record adjustments as necessary for changed circumstances and customer-specific information.  When specific receivables are determined to be uncollectible, the reserve and receivable are relieved.
 
Inventories
 
Our inventories of products consist of natural gas liquids, refined petroleum products, natural gas, and carbon dioxide.  We report these assets at the lower of weighted-average cost or market. We report materials and supplies inventories at cost, and periodically review for physical deterioration and obsolescence.
 
Gas Imbalances
 
We value gas imbalances due to or due from interconnecting pipelines at the lower of cost or market, per our quarterly imbalance valuation procedures.  Gas imbalances represent the difference between customer nominations and actual gas receipts from, and gas deliveries to, our interconnecting pipelines and shippers under various operational balancing and shipper imbalance agreements.  Natural gas imbalances are either settled in cash or made up in-kind subject to the pipelines’ various tariff provisions.  As of December 31, 2012 and 2011, our gas imbalance receivables—including both trade and related party receivables—totaled $13 million and $19 million, respectively, and we included these amounts within “Other current assets” on our accompanying consolidated balance sheets.  As of December 31, 2012 and 2011, our gas imbalance payables—including both trade and related party payables—totaled $43 million and $9 million, respectively, and we included these amounts within “Accrued other current liabilities” on our accompanying consolidated balance sheets.
 
Property, Plant and Equipment
 
Capitalization, Depreciation and Depletion and Disposals
 
We report property, plant and equipment at its acquisition cost.  We expense costs for maintenance and repairs in the period incurred.  As discussed below, for assets used in our oil and gas producing activities or in our unregulated bulk and liquids terminal activities, the cost of property, plant and equipment sold or retired and the related depreciation are removed from our balance sheet in the period of sale or disposition, and we record any related gains and losses from sales or retirements to income or expense accounts.  For our pipeline system assets, we generally charge the original cost of property sold or retired to accumulated depreciation and amortization, net of salvage and cost of removal.  We do not include retirement gain or loss in income except in the case of significant retirements or sales.  Gains and losses on minor system sales, excluding land, are recorded to the appropriate accumulated depreciation reserve.  Gains and losses for operating systems sales and land sales are booked to income or expense accounts in accordance with regulatory accounting guidelines.
 
We generally compute depreciation using the straight-line method based on estimated economic lives; however, for certain depreciable assets, we employ the composite depreciation method, applying a single depreciation rate for a group of assets.  Generally, we apply composite depreciation rates to functional groups of property having similar economic characteristics.  The rates range from 1.6% to 12.5%, excluding certain short-lived assets such as vehicles.  Depreciation estimates are based on various factors, including age (in the case of acquired assets), manufacturing specifications, technological advances and historical data concerning useful lives of similar assets.  Uncertainties that impact these estimates included changes in laws and regulations relating to restoration and abandonment requirements, economic conditions, and supply and demand in the area.  When assets are put into service, we make estimates with respect to useful lives (and salvage values where appropriate) that we believe are reasonable.  However, subsequent events could cause us to change our estimates, thus impacting the future calculation of depreciation and amortization expense.  Historically, adjustments to useful lives have not had a material impact on our aggregate depreciation levels from year to year.

Our oil and gas producing activities are accounted for under the successful efforts method of accounting.  Under this method costs that are incurred to acquire leasehold and subsequent development costs are capitalized.  Costs that are associated with the drilling of successful exploration wells are capitalized if proved reserves are found.  Costs associated with the drilling of exploratory wells that do not find proved reserves, geological and geophysical costs, and costs of certain non-producing leasehold costs are expensed as incurred.  The capitalized costs of our producing oil and gas properties are depreciated and depleted by the units-of-production method.  Other miscellaneous property, plant and equipment are depreciated over the estimated useful lives of the asset.
 
A gain on the sale of property, plant and equipment used in our oil and gas producing activities or in our bulk and liquids terminal activities is calculated as the difference between the cost of the asset disposed of, net of depreciation, and the sales proceeds received.  A gain on an asset disposal is recognized in income in the period that the sale is closed.  A loss on the sale of property, plant and equipment is calculated as the difference between the cost of the asset disposed of, net of depreciation, and the sales proceeds received or the market value if the asset is being held for sale.  A loss is recognized when the asset is sold or when the net cost of an asset held for sale is greater than the market value of the asset.
 
In addition, we engage in enhanced recovery techniques in which carbon dioxide is injected into certain producing oil reservoirs.  In some cases, the acquisition cost of the carbon dioxide associated with enhanced recovery is capitalized as part of our development costs when it is injected.  The acquisition cost associated with pressure maintenance operations for reservoir management is expensed when it is injected.  When carbon dioxide is recovered in conjunction with oil production, it is extracted and re-injected, and all of the associated costs are expensed as incurred.  Proved developed reserves are used in computing units of production rates for drilling and development costs, and total proved reserves are used for depletion of leasehold costs.  The units-of-production rate is determined by field.
 
As discussed in “—Inventories” above, we own and maintain natural gas in underground storage as part of our inventory. This component of our inventory represents the portion of gas stored in an underground storage facility generally known as working gas, and represents an estimate of the portion of gas in these facilities available for routine injection and withdrawal. In addition to this working gas, underground gas storage reservoirs contain injected gas which is not routinely cycled but, instead, serves the function of maintaining the necessary pressure to allow efficient operation of the facility.  This gas, generally known as cushion gas, is divided into the categories of recoverable cushion gas and unrecoverable cushion gas, based on an engineering analysis of whether the gas can be economically removed from the storage facility at any point during its life.  The portion of the cushion gas that is determined to be unrecoverable is considered to be a permanent part of the facility itself (thus, part of our “Property, plant and equipment, net” balance in our accompanying consolidated balance sheets), and this unrecoverable portion is depreciated over the facility’s estimated useful life.  The portion of the cushion gas that is determined to be recoverable is also considered a component of the facility but is not depreciated because it is expected to ultimately be recovered and sold.

Impairments
 
We measure long-lived assets that are to be disposed of by sale at the lower of book value or fair value less the cost to sell, and we review for the impairment of long-lived assets whenever events or changes in circumstances indicate that our carrying amount of an asset may not be recoverable.  We would recognize an impairment loss when estimated future cash flows expected to result from our use of the asset and its eventual disposition is less than its carrying amount.
 
We evaluate our oil and gas producing properties for impairment of value on a field-by-field basis or, in certain instances, by logical grouping of assets if there is significant shared infrastructure, using undiscounted future cash flows based on total proved and risk-adjusted probable and possible reserves.  For the purpose of impairment testing, adjustments for the inclusion of risk-adjusted probable and possible reserves, as well as forward curve pricing, will cause impairment calculation cash flows to differ from the amounts presented in our supplemental information on oil and gas producing activities disclosed in “Supplemental Information on Oil and Gas Activities (Unaudited)” included elsewhere in this report.
 
Oil and gas producing properties deemed to be impaired are written down to their fair value, as determined by discounted future cash flows based on total proved and risk-adjusted probable and possible reserves or, if available, comparable market values.  Unproved oil and gas properties that are individually significant are periodically assessed for impairment of value, and a loss is recognized at the time of impairment.
 
Asset Retirement Obligations
 
We record liabilities for obligations related to the retirement and removal of long-lived assets used in our businesses.  We record, as liabilities, the fair value of asset retirement obligations on a discounted basis when they are incurred, which is typically at the time the assets are installed or acquired.  Amounts recorded for the related assets are increased by the amount of these obligations.  Over time, the liabilities increase due to the change in their present value, and the initial capitalized costs are depreciated over the useful lives of the related assets.  The liabilities are eventually extinguished when the asset is taken out of service.  For more information on our asset retirement obligations, see Note 5 “Property, Plant and Equipment—Asset Retirement Obligations.”
 
Equity Method of Accounting

We account for investments—which we do not control but do have the ability to exercise significant influence—by the equity method of accounting.  Under this method, our equity investments are carried originally at our acquisition cost, increased by our proportionate share of the investee’s net income and by contributions made, and decreased by our proportionate share of the investee’s net losses and by distributions received.
 
Goodwill
 
Goodwill represents the excess of the cost of an acquisition price over the fair value of acquired net assets, and such amounts are reported separately as “Goodwill” on our accompanying consolidated balance sheets.  Our total goodwill was $4,606 million as of December 31, 2012, and $1,436 million as of December 31, 2011.  Goodwill cannot be amortized, but instead must be tested for impairment annually or on an interim basis if events or circumstances indicate that the fair value of the asset has decreased below its carrying value.
 
We perform our goodwill impairment test on May 31 of each year.  There were no impairment charges resulting from our May 31, 2012, 2011 or 2010 impairment testing, and no event indicating an impairment has occurred subsequent to May 31, 2012.

If a significant portion of one of our business segments is disposed of (that also constitutes a business), we would allocate goodwill based on the relative fair values of the portion of the segment being disposed of and the portion of the segment remaining.  For more information on our goodwill, see Note 7.
 
Revenue Recognition Policies
 
We recognize revenues as services are rendered or goods are delivered and, if applicable, title has passed.  We generally sell natural gas under long-term agreements, generally based on Houston Ship Channel index posted prices.  In some cases, we sell natural gas under short-term agreements at prevailing market prices.  In all cases, we recognize natural gas sales revenues when the natural gas is sold to a purchaser at a fixed or determinable price, delivery has occurred and title has transferred, and collectability of the revenue is reasonably assured.  The natural gas we market is primarily purchased gas produced by third parties, and we market this gas to power generators, local distribution companies, industrial end-users and national marketing companies.  We recognize gas gathering and marketing revenues in the month of delivery based on customer nominations and generally, our natural gas marketing revenues are recorded gross, not net of cost of gas sold.
 
In addition to storing and transporting a significant portion of the natural gas volumes we purchase and resell, we provide various types of natural gas storage and transportation services for third-party customers.  The natural gas remains the property of these customers at all times.  In many cases, generally described as firm service, the customer pays a two-part rate that includes (i) a fixed fee reserving the right to transport or store natural gas in our facilities; and (ii) a per-unit rate for volumes actually transported or injected into/withdrawn from storage.  The fixed-fee component of the overall rate is recognized as revenue in the period the service is provided.  The per-unit charge is recognized as revenue when the volumes are delivered to the customers’ agreed upon delivery point, or when the volumes are injected into/withdrawn from our storage facilities.
 
In other cases, generally described as interruptible service, there is no fixed fee associated with the services because the customer accepts the possibility that service may be interrupted at our discretion in order to serve customers who have purchased firm service.  In the case of interruptible service, revenue is recognized in the same manner utilized for the per-unit rate for volumes actually transported under firm service agreements.  
 
We provide crude oil transportation services and refined petroleum products transportation and storage services to customers.  Revenues are recorded when products are delivered and services have been provided, and adjusted according to terms prescribed by the toll settlements with shippers and approved by regulatory authorities.
 
We recognize bulk terminal transfer service revenues based on volumes loaded and unloaded.  We recognize liquids terminal tank rental revenue ratably over the contract period.  We recognize liquids terminal throughput revenue based on volumes received and volumes delivered.  Liquids terminal minimum take-or-pay revenue is recognized at the end of the contract year or contract term depending on the terms of the contract.  We recognize transmix processing revenues based on volumes processed or sold, and if applicable, when title has passed.  We recognize energy-related product sales revenues based on delivered quantities of product.
 
Revenues from the sale of crude oil, natural gas liquids, carbon dioxide and natural gas production are recorded using the entitlement method.  Under the entitlement method, revenue is recorded when title passes based on our net interest.  We record our entitled share of revenues based on entitled volumes and contracted sales prices.  Since there is a ready market for oil and gas production, we sell the majority of our products soon after production at various locations, at which time title and risk of loss pass to the buyer.  As a result, we maintain a minimum amount of product inventory in storage.
 
Environmental Matters
 
We expense or capitalize, as appropriate, environmental expenditures that relate to current operations.  We expense expenditures that relate to an existing condition caused by past operations, which do not contribute to current or future revenue generation.  We generally do not discount environmental liabilities to a net present value, and we record environmental liabilities when environmental assessments and/or remedial efforts are probable and we can reasonably estimate the costs. Generally, our recording of these accruals coincides with our completion of a feasibility study or our commitment to a formal plan of action.  We recognize receivables for anticipated associated insurance recoveries when such recoveries are deemed to be probable. We record at fair value, where appropriate, environmental liabilities assumed in a business combination.

We routinely conduct reviews of potential environmental issues and claims that could impact our assets or operations. These reviews assist us in identifying environmental issues and estimating the costs and timing of remediation efforts.  We also routinely adjust our environmental liabilities to reflect changes in previous estimates.  In making environmental liability estimations, we consider the material effect of environmental compliance, pending legal actions against us, and potential third-party liability claims.  Often, as the remediation evaluation and effort progresses, additional information is obtained, requiring revisions to estimated costs.  These revisions are reflected in our income in the period in which they are reasonably determinable.  For more information on our environmental disclosures, see Note 16.
 
Legal
 
We are subject to litigation and regulatory proceedings as the result of our business operations and transactions.  We utilize both internal and external counsel in evaluating our potential exposure to adverse outcomes from orders, judgments or settlements.  When we identify specific litigation that is expected to continue for a significant period of time, is reasonably possible to occur, and may require substantial expenditures, we identify a range of possible costs expected to be required to litigate the matter to a conclusion or reach an acceptable settlement, and we accrue for such amounts.  To the extent that actual outcomes differ from our estimates, or additional facts and circumstances cause us to revise our estimates, our earnings will be affected.  In general, we expense legal costs as incurred and all recorded legal liabilities are revised as better information becomes available.  For more information on our legal disclosures, see Note 16.
 
Pensions and Other Postretirement Benefits  
 
We fully recognize the overfunded or underfunded status of our consolidating subsidiaries’ pension and other postretirement benefit plans as either assets or liabilities on our balance sheet.  A plan’s funded status is the difference between the fair value of plan assets and the plan’s benefit obligation.  We record deferred plan costs and income—unrecognized losses and gains, unrecognized prior service costs and credits, and any remaining unamortized transition obligations—in accumulated other comprehensive income, until they are amortized to expense.  For more information on our pension and postretirement benefit disclosures, see Note 9.
 
Noncontrolling Interests
 
Noncontrolling interests represents the outstanding ownership interests in our five operating limited partnerships and their consolidated subsidiaries that are not owned by us.  In our accompanying consolidated income statements, the noncontrolling interest in the net income (or loss) of our consolidated subsidiaries is shown as an allocation of our consolidated net income and is presented separately as “Net Income Attributable to Noncontrolling Interests.”  In our accompanying consolidated balance sheets, noncontrolling interests represents the ownership interests in our consolidated subsidiaries’ net assets held by parties other than us.  It is presented separately as “Noncontrolling interests” within “Partners’ Capital.”
 
As of December 31, 2011, our noncontrolling interests consisted of the following: (i) the 1.0101% general partner interest in each of our five operating partnerships; (ii) the 0.5% special limited partner interest in SFPP, L.P.; (iii) the 33 1/3% interest in International Marine Terminals Partnership, a Louisiana partnership; (iv) the approximate 31% interest in the Pecos Carbon Dioxide Company, a Texas general partnership; (v) the 35% interest in Guilford County Terminal Company, LLC, a limited liability company; (vi) a 2.5% interest in Battleground Oil Specialty Terminal Company LLC (BOSTCO), a limited liability company; and (vii) the 50% interest in Globalplex Partners, a Louisiana joint venture. In addition to the above, our noncontrolling interests as of December 31, 2012 included (i) an additional 42.5% interest in BOSTCO; and (ii) the 49% interest in Deeprock Development LLC, a limited liability company.

Income Taxes
 
We are not a taxable entity for federal income tax purposes.  As such, we do not directly pay federal income tax.  Our taxable income or loss, which may vary substantially from the net income or net loss we report in our consolidated statement of income, is includable in the federal income tax returns of each partner.  The aggregate difference in the basis of our net assets for financial and tax reporting purposes cannot be readily determined as we do not have access to information about each partner’s tax attributes in us.
 
Some of our corporate subsidiaries and corporations in which we have an equity investment do pay U.S. federal, state, and foreign income taxes.  Deferred income tax assets and liabilities for certain operations conducted through corporations are recognized for temporary differences between the assets and liabilities for financial reporting and tax purposes.  Changes in tax legislation are included in the relevant computations in the period in which such changes are effective.  Deferred tax assets are reduced by a valuation allowance for the amount of any tax benefit not expected to be realized.  For more information on our income tax disclosures, see Note 4.
 
Foreign Currency Transactions and Translation
 
Foreign currency transactions are those transactions whose terms are denominated in a currency other than the currency of the primary economic environment in which our reporting subsidiary operates, also referred to as its functional currency. Transaction gains or losses result from a change in exchange rates between (i) the functional currency, for example the Canadian dollar for a Canadian subsidiary; and (ii) the currency in which a foreign currency transaction is denominated, for example the U.S. dollar for a Canadian subsidiary.  In our accompanying consolidated statements of income, gains and losses from our foreign currency transactions are included within “Other Income (Expense)—Other, net.”
 
Foreign currency translation is the process of expressing, in U.S. dollars, amounts denominated or measured in a different local functional currency, for example the Canadian dollar for a Canadian subsidiary.  We translate the assets and liabilities of each of our consolidating foreign subsidiaries that have a local functional currency to U.S. dollars at year-end exchange rates. Income and expense items are translated at weighted-average rates of exchange prevailing during the year and partners’ capital equity accounts are translated by using historical exchange rates.  Translation adjustments result from translating all assets and liabilities at current year-end rates, while partners’ capital equity is translated by using historical and weighted-average rates.  The cumulative translation adjustments balance is reported as a component of “Accumulated other comprehensive income” within “Partners’ Capital” in our consolidated balance sheets.
 
Comprehensive Income
 
For each of the years ended December 31, 2012, 2011 and 2010, the difference between our net income and our comprehensive income resulted from (i) unrealized gains or losses on derivative contracts utilized for hedging our exposure to fluctuating expected future cash flows produced by both energy commodity price risk and interest rate risk; (ii) foreign currency translation adjustments; and (iii) unrealized gains or losses related to changes in pension and other postretirement benefit plan liabilities.  For more information on our risk management activities, see Note 13.
 
Cumulative revenues, expenses, gains and losses that under U.S. generally accepted accounting principles are included within our comprehensive income but excluded from our earnings are reported as “Accumulated other comprehensive income” within “Partners’ Capital” in our consolidated balance sheets.  The following table summarizes changes in the amount of our “Accumulated other comprehensive income (loss)” in our accompanying consolidated balance sheets for each of the years ended December 31, 2012 and 2011 (in millions):
 
Net unrealized
gains/(losses)
on cash flow
hedge derivatives
 
Foreign
currency
translation
adjustments
 
Pension and
other
postretirement
liability adjs.
 
Total
Accumulated other
comprehensive
income/(loss)
December 31, 2010
$
(308
)
 
$
132

 
$
(10
)
 
$
(186
)
Change for period
267

 
(44
)
 
(34
)
 
189

December 31, 2011
(41
)
 
88

 
(44
)
 
3

Change for period
107

 
44

 
9

 
160

December 31, 2012
$
66

 
$
132

 
$
(35
)
 
$
163


 
Limited Partners’ Net Income per Unit
 
We compute Limited Partners’ Net Income per Unit by dividing our limited partners’ interest in net income by the weighted average number of units outstanding during the period.  The overall computation, presentation, and disclosure requirements for our Limited Partners’ Net Income per Unit  are made in accordance with the “Earnings per Share” Topic of the Codification.

Risk Management Activities
 
We utilize energy commodity derivative contracts for the purpose of mitigating our risk resulting from fluctuations in the market price of natural gas, natural gas liquids and crude oil.  In addition, we enter into interest rate swap agreements for the purpose of hedging the interest rate risk associated with our debt obligations.  We measure our derivative contracts at fair value and we report them on our balance sheet as either an asset or liability.  If the derivative transaction qualifies for and is designated as a normal purchase and sale, it is exempted from fair value accounting and is accounted for using traditional accrual accounting.

Furthermore, changes in our derivative contracts’ fair values are recognized currently in earnings unless specific hedge accounting criteria are met.  If a derivative contract meets those criteria, the contract’s gains and losses are allowed to offset related results on the hedged item in our income statement, and we are required to both formally designate the derivative contract as a hedge and document and assess the effectiveness of the contract associated with the transaction that receives hedge accounting.  Only designated qualifying items that are effectively offset by changes in fair value or cash flows during the term of the hedge are eligible to use the special accounting for hedging.
 
Our derivative contracts that hedge our energy commodity price risks involve our normal business activities, which include the sale of natural gas, natural gas liquids and crude oil, and we have designated these derivative contracts as cash flow hedges—derivative contracts that hedge exposure to variable cash flows of forecasted transactions—and the effective portion of these derivative contracts’ gain or loss is initially reported as a component of other comprehensive income (outside earnings) and subsequently reclassified into earnings when the forecasted transaction affects earnings.  The ineffective portion of the gain or loss is reported in earnings immediately.  See Note 13 for more information on our risk management activities and disclosures.
 
Accounting for Regulatory Activities
 
Regulatory assets and liabilities represent probable future revenues or expenses associated with certain charges and credits that will be recovered from or refunded to customers through the ratemaking process.  The amount of our regulatory assets and liabilities totaled $180 million and $21 million, respectively, as of December 31, 2012, and totaled $15 million and $12 million, respectively, as of December 31, 2011. We included the amounts of our regulatory assets and liabilities within “Other current assets,” “Deferred charges and other assets,” “Accrued other current liabilities” and “Other long-term liabilities and deferred credits,” respectively, in our accompanying consolidated balance sheets as of December 31, 2012 and 2011. The overall increase in our total regulatory assets since December 31, 2011 was primarily due to a $113 million increase associated with an expected loss on TGP assets currently held for sale. We expect to recover this loss through TGP’s jurisdictional natural gas transportation rates. The recovery period for this regulatory asset is approximately 20 years.