Basis of Presentation and Summary of Significant Accounting Policies	12 Months Ended
Dec. 31, 2014
Accounting Policies [Abstract]
Basis of Presentation and Summary of Significant Accounting Policies	Basis of Presentation and Summary of Significant Accounting Policies Basis of Presentation We are an integrated communications company engaged primarily in providing an array of communications services to our residential, business, governmental and wholesale customers. Our communications services include local and long-distance, broadband, private line (including special access), Multi-Protocol Label Switching ("MPLS"), data integration, managed hosting (including cloud hosting), colocation, Ethernet, network access, public access, wireless, video and other ancillary services. The accompanying consolidated financial statements include our accounts and the accounts of our subsidiaries. Intercompany amounts and transactions with our consolidated subsidiaries have been eliminated. To simplify the overall presentation of our consolidated financial statements, we report immaterial amounts attributable to noncontrolling interests in certain of our subsidiaries as follows: (i) income attributable to noncontrolling interests in other income (expense), (ii) equity attributable to noncontrolling interests in additional paid-in capital and (iii) cash flows attributable to noncontrolling interests in other, net financing activities. We reclassified certain prior period amounts to conform to the current period presentation, including the categorization of our revenues and our segment reporting. See Note 12—Segment Information for additional information. These changes had no impact on total revenues, total operating expenses or net income (loss) for any period. In January 2013, we sold $43 million of our wireless spectrum assets held for sale. The sale resulted in a gain of $32 million, which is recorded as other income on our consolidated statements of operations. Changes in Estimates As a result of our annual reviews to evaluate the reasonableness of the depreciable lives for our property, plant and equipment, effective January 2014, we changed the estimates of the remaining economic lives of certain switch and circuit network equipment. These changes resulted in a net increase in depreciation expense of approximately $78 million for the year ended December 31, 2014. This net increase in depreciation expense, net of tax, reduced consolidated net income by approximately $48 million, or $0.08 per basic and diluted common share, for the year ended December 31, 2014. Additionally, during the third quarter of 2014, we developed a plan to migrate customers from one of our networks to another between the fourth quarter of 2014 through the fourth quarter of 2015. As a result, we implemented changes in estimates that reduced the remaining economic lives of certain network assets. These changes increased depreciation expense of approximately $12 million for the year ended December 31, 2014 and is expected to increase depreciation expense by approximately $48 million for 2015. The increase in depreciation expense, net of tax, reduced consolidated net income by approximately $7 million, or $0.01 per basic and diluted common share, for the year ended December 31, 2014. During the fourth quarter 2013, we changed the estimates of the remaining economic lives of certain intangible assets, specifically, the Savvis trade name, which is no longer being utilized, and certain Savvis cloud software, which has been replaced by cloud software acquired through our more recent acquisitions. These changes resulted in an increase in amortization expense of approximately $23 million for the year ended December 31, 2014. This increase in amortization expense, net of tax, reduced consolidated net income by approximately $14 million, or $0.02 per basic and diluted common share, for the year ended December 31, 2014. As of December 31, 2014, the Savvis trade name and the Savvis cloud software were fully amortized. Summary of Significant Accounting Policies Use of Estimates Our consolidated financial statements are prepared in accordance with U.S. generally accepted accounting principles. These accounting principles require us to make certain estimates, judgments and assumptions. We believe that the estimates, judgments and assumptions we make when accounting for items and matters such as, but not limited to, investments, long-term contracts, customer retention patterns, allowance for doubtful accounts, depreciation, amortization, asset valuations, internal labor capitalization rates, recoverability of assets (including deferred tax assets), impairment assessments, pension, post-retirement and other post-employment benefits, taxes, certain liabilities and other provisions and contingencies are reasonable, based on information available at the time they were made. These estimates, judgments and assumptions can affect the reported amounts of assets, liabilities and components of stockholders' equity as of the dates of the consolidated balance sheets, as well as the reported amounts of revenues, expenses and components of cash flows during the periods presented in our consolidated statements of operations, our consolidated statements of comprehensive (loss) income and our consolidated statements of cash flows. We also make estimates in our assessments of potential losses in relation to threatened or pending tax and legal matters. See Note 11—Income Taxes and Note 14—Commitments and Contingencies for additional information. For matters not related to income taxes, if a loss is considered probable and the amount can be reasonably estimated, we recognize an expense for the estimated loss. If we have the potential to recover a portion of the estimated loss from a third party, we make a separate assessment of recoverability and reduce the estimated loss if recovery is also deemed probable. For matters related to income taxes, if we determine that the impact of an uncertain tax position is more likely than not to be sustained upon audit by the relevant taxing authority, then we recognize a benefit for the largest amount that is more likely than not to be sustained. No portion of an uncertain tax position will be recognized if the position has less than a 50% likelihood of being sustained. Interest is recognized on the amount of unrecognized benefit from uncertain tax positions. For all of these and other matters, actual results could differ from our estimates. Revenue Recognition We recognize revenue for services when the related services are provided. Recognition of certain payments received in advance of services being provided is deferred until the service is provided. These advance payments include activation and installation charges, which we recognize as revenue over the expected customer relationship period, which ranges from eighteen months to over ten years depending on the service. We also defer costs for customer activations and installations. The deferral of customer activation and installation costs is limited to the amount of revenue deferred on advance payments. Costs in excess of advance payments are recorded as expense in the period such costs are incurred. Expected customer relationship periods are estimated using historical experience. Termination fees or other fees on existing contracts that are negotiated in conjunction with new contracts are deferred and recognized over the new contract term. We offer bundle discounts to our customers who receive certain groupings of services. These bundle discounts are recognized concurrently with the associated revenue and are allocated to the various services in the bundled offering based on the estimated selling price of services included in each bundled combination. Customer arrangements that include both equipment and services are evaluated to determine whether the elements are separable. If the elements are deemed separable and separate earnings processes exist, the revenue associated with the customer arrangement is allocated to each element based on the relative estimated selling price of the separate elements. We have estimated the selling prices of each element by reference to vendor-specific objective evidence of selling prices when the elements are sold separately. The revenue associated with each element is then recognized as earned. For example, if we receive an advance payment when we sell equipment and continuing service together, we immediately recognize as revenue the amount allocated to the equipment as long as all the conditions for revenue recognition have been satisfied. The portion of the advance payment allocated to the service based upon its relative selling price is recognized ratably over the longer of the contractual period or the expected customer relationship period. We periodically transfer optical capacity assets on our network to other telecommunications service carriers. These transactions are structured as indefeasible rights of use, commonly referred to as IRUs, which are the exclusive right to use a specified amount of capacity or fiber for a specified term, typically 20 years. We account for the cash consideration received on transfers of optical capacity assets and on all of the other elements deliverable under an IRU, as revenue ratably over the term of the agreement. We have not recognized revenue on any contemporaneous exchanges of our optical capacity assets for other optical capacity assets. In connection with offering products and services provided by third-party vendors, we review the relationship between us, the vendor and the end customer to assess whether revenue should be reported on a gross or net basis. In assessing whether revenue should be reported on a gross or net basis, we consider whether we act as a principal in the transaction, take title to the products, have risk and rewards of ownership or act as an agent or broker. Based on our agreements with DIRECTV and Verizon Wireless, we offer these services through sales agency relationships which are reported on a net basis. For our hosting operations, we have service level commitments pursuant to contracts with certain of our clients. To the extent that such service levels are not achieved or are otherwise disputed due to performance or service issues or other service interruptions or conditions, we will estimate the amount of credits to be issued and record a reduction to revenues, with a corresponding increase in the credit reserve. USF, Gross Receipts Taxes and Other Surcharges In determining whether to include in our revenues and expenses the taxes and surcharges collected from customers and remitted to government authorities, including USF charges, sales, use, value added and some excise taxes, we assess, among other things, whether we are the primary obligor or principal taxpayer for the taxes assessed in each jurisdiction where we do business. In jurisdictions where we determine that we are the principal taxpayer, we record the surcharges on a gross basis and include them in our revenues and costs of services and products. In jurisdictions where we determine that we are merely a collection agent for the government authority, we record the taxes on a net basis and do not include them in our revenues and costs of services and products. Advertising Costs Costs related to advertising are expensed as incurred and included in selling, general and administrative expenses in our consolidated statements of operations. Our advertising expense was $214 million, $210 million and $189 million for the years ended December 31, 2014, 2013 and 2012, respectively. Legal Costs In the normal course of our business, we incur costs to hire and retain external legal counsel to advise us on regulatory, litigation and other matters. We expense these costs as the related services are received. Income Taxes We file a consolidated federal income tax return with our eligible subsidiaries. The provision for income taxes consists of an amount for taxes currently payable, an amount for tax consequences deferred to future periods, adjustments to our liabilities for uncertain tax positions and amortization of investment tax credits. We record deferred income tax assets and liabilities reflecting future tax consequences attributable to tax net operating losses ("NOLs"), tax credit carryforwards and differences between the financial statement carrying value of assets and liabilities and the tax bases of those assets and liabilities. Deferred taxes are computed using enacted tax rates expected to apply in the year in which the differences are expected to affect taxable income. The effect on deferred income tax assets and liabilities of a change in tax rate is recognized in earnings in the period that includes the enactment date. We establish valuation allowances when necessary to reduce deferred income tax assets to the amounts that we believe are more likely than not to be recovered. A significant portion of our net deferred tax assets relate to tax benefits attributable to NOLs. Each quarter we evaluate the need to retain all or a portion of the valuation allowance on our deferred tax assets. See Note 11—Income Taxes for additional information. Cash and Cash Equivalents Cash and cash equivalents include highly liquid investments that are readily convertible into cash and are not subject to significant risk from fluctuations in interest rates. As a result, the value at which cash and cash equivalents are reported in our consolidated financial statements approximates their fair value. In evaluating investments for classification as cash equivalents, we require that individual securities have original maturities of ninety days or less and that individual investment funds have dollar-weighted average maturities of ninety days or less. To preserve capital and maintain liquidity, we invest with financial institutions we deem to be of sound financial condition and in high quality and relatively risk-free investment products. Our cash investment policy limits the concentration of investments with specific financial institutions or among certain products and includes criteria related to credit worthiness of any particular financial institution. Book overdrafts occur when checks have been issued but have not been presented to our controlled disbursement bank accounts for payment. Disbursement bank accounts allow us to delay funding of issued checks until the checks are presented for payment. Until the issued checks are presented for payment, the book overdrafts are included in accounts payable on our consolidated balance sheet. This activity is included in the operating activities section in our consolidated statements of cash flows. Accounts Receivable and Allowance for Doubtful Accounts Accounts receivable are recognized based upon the amount due from customers for the services provided or at cost for purchased and other receivables less an allowance for doubtful accounts. The allowance for doubtful accounts receivable reflects our best estimate of probable losses inherent in our receivable portfolio determined on the basis of historical experience, specific allowances for known troubled accounts and other currently available evidence. We generally consider our accounts past due if they are outstanding over 30 days. Our collection process varies by the customer segment, amount of the receivable, and our evaluation of the customer's credit risk. Our past due accounts are written off against our allowance for doubtful accounts when collection is considered to be not probable. Any recoveries of accounts previously written off are generally recognized as a reduction in bad debt expense in the period received. The carrying value of accounts receivable net of the allowance for doubtful accounts approximates fair value. Property, Plant and Equipment Property, plant and equipment acquired in connection with our acquisitions was recorded based on its estimated fair value as of its acquisition date plus the estimated value of any associated legally or contractually required retirement obligations. Purchased and constructed property, plant and equipment is recorded at cost, plus the estimated value of any associated legally or contractually required retirement obligations. Property, plant and equipment is depreciated primarily using the straight-line group method. Under the straight-line group method, assets dedicated to providing telecommunications services (which comprise the majority of our property, plant and equipment) that have similar physical characteristics, use and expected useful lives are pooled for purposes of depreciation and tracking. The equal life group procedure is used to establish each pool's average remaining useful life. Generally, under the straight-line group method, when an asset is sold or retired in the course of normal business activities, the cost is deducted from property, plant and equipment and charged to accumulated depreciation without recognition of a gain or loss. A gain or loss is recognized in our consolidated statements of operations only if a disposal is abnormal or unusual. Leasehold improvements are amortized over the shorter of the useful lives of the assets or the expected lease term. Expenditures for maintenance and repairs are expensed as incurred. Interest is capitalized during the construction phase of network and other internal-use capital projects. Employee-related costs for construction of network and other internal use assets are also capitalized during the construction phase. Property, plant and equipment supplies used internally are carried at average cost, except for significant individual items for which cost is based on specific identification. We perform annual internal reviews to evaluate the reasonableness of the depreciable lives for our property, plant and equipment. Our reviews utilize models that take into account actual usage, physical wear and tear, replacement history, assumptions about technology evolution and, in certain instances, actuarially determined probabilities to estimate the remaining useful life of our asset base. Our remaining useful life assessments anticipate the loss in service value of assets that may precede the physical retirement. Assets shared among many customers may lose service value as those customers leave the network. However, the asset is not retired until all customers no longer utilize the asset. We have asset retirement obligations associated with the legally or contractually required removal of a limited group of property, plant and equipment assets from leased properties and the disposal of certain hazardous materials present in our owned properties. When an asset retirement obligation is identified, usually in association with the acquisition of the asset, we record the fair value of the obligation as a liability. The fair value of the obligation is also capitalized as property, plant and equipment and then amortized over the estimated remaining useful life of the associated asset. Where the removal obligation is not legally binding, the net cost to remove assets is expensed in the period in which the costs are actually incurred. We review long-lived tangible assets for impairment whenever facts and circumstances indicate that the carrying amounts of the assets may not be recoverable. For assessment purposes, long-lived assets are grouped with other assets and liabilities at the lowest level for which identifiable cash flows are largely independent of the cash flows of other assets and liabilities, absent a material change in operations. An impairment loss is recognized only if the carrying amount of the asset group is not recoverable and exceeds its fair value. Recoverability of the asset group to be held and used is assessed by comparing the carrying amount of the asset group to the estimated undiscounted future net cash flows expected to be generated by the asset group. If the asset group's carrying value is not recoverable, an impairment charge is recognized for the amount by which the carrying amount of the asset group exceeds its fair value. We determine fair values by using a combination of comparable market values and discounted cash flows, as appropriate. Goodwill, Customer Relationships and Other Intangible Assets Intangible assets arising from business combinations, such as goodwill, customer relationships, capitalized software, trademarks and trade names, are initially recorded at estimated fair value. We amortize customer relationships primarily over an estimated life of 10 to 15 years, using either the sum-of-the-years-digits or the straight-line methods, depending on the type of customer. We amortize capitalized software using the straight-line method over estimated lives ranging up to 7 years, except for approximately $237 million of our capitalized software costs, which represents costs to develop an integrated billing and customer care system which is amortized using the straight-line method over a 20 year period. We amortize our other intangible assets predominantly using the sum-of-the-years-digits method over an estimated life of 4 years. Other intangible assets not arising from business combinations are initially recorded at cost. Where there are no legal, regulatory, contractual or other factors that would reasonably limit the useful life of an intangible asset, we classify the intangible asset as indefinite-lived and such intangible assets are not amortized. Internally used software, whether purchased or developed by us, is capitalized and amortized using the straight-line method over its estimated useful life. We have capitalized certain costs associated with software such as costs of employees devoting time to the projects and external direct costs for materials and services. Costs associated with software to be used for internal purposes are expensed until the point at which the project has reached the development stage. Subsequent additions, modifications or upgrades to internal-use software are capitalized only to the extent that they allow the software to perform a task it previously did not perform. Software maintenance, data conversion and training costs are expensed in the period in which they are incurred. We review the remaining economic lives of our capitalized software annually. Capitalized software is included in other intangible assets, net, in our consolidated balance sheets. Our long-lived intangible assets, other than goodwill, with indefinite lives are assessed for impairment annually, or, under certain circumstances, more frequently, such as when events or circumstances indicate there may be an impairment. These assets are carried at the estimated fair value at the time of acquisition and assets not acquired in acquisitions are recorded at historical cost. However, if their estimated fair value is less than the carrying amount, other indefinite-lived intangible assets are reduced to their estimated fair value through an impairment charge to our consolidated statements of operations. We annually review the estimated lives and methods used to amortize our other intangible assets. The actual amounts of amortization expense may differ materially from our estimates, depending on the results of our annual review. We are required to assess goodwill for impairment at least annually, or more frequently if events or a change in circumstances indicate that an impairment may have occurred. We are required to write-down the value of goodwill in periods in which the recorded amount of goodwill exceeds the implied fair value of goodwill. Our reporting units are not discrete legal entities with discrete financial statements. Our assets and liabilities are employed in and relate to the operations of multiple reporting units. Therefore, the equity carrying value and future cash flows must be estimated each time a goodwill impairment assessment is performed on a reporting unit. As a result, our assets, liabilities and cash flows are assigned to reporting units using reasonable and consistent allocation methodologies. Certain estimates, judgments and assumptions are required to perform these assignments. We believe these estimates, judgments and assumptions to be reasonable, but changes in many of these can significantly affect each reporting unit's equity carrying value and future cash flows utilized for our goodwill impairment assessment. During the fourth quarter of 2013, we elected to change the date of our annual assessment of goodwill impairment from September 30 to October 31. This is a change in method of applying an accounting principle which management believes is a preferable alternative as the new date of the assessment is more closely aligned with our strategic planning process. The change in the assessment date did not delay, accelerate or avoid a potential impairment charge in 2013. We performed our annual goodwill impairment assessment at September 30, 2013, prior to the change in our annual assessment date. We then performed a qualitative assessment of our goodwill as of October 31, 2013 and concluded that our goodwill for consumer, wholesale and business reporting units was not impaired and our goodwill for hosting reporting unit was not further impaired as of that date. We are required to reassign goodwill to reporting units each time we reorganize our internal reporting structure which causes a change in the composition of our reporting units. Goodwill is reassigned to the reporting units using a relative fair value approach. We utilize the earnings before interest, taxes, depreciation and amortization as our allocation methodology as it represents a reasonable proxy for the fair value of the operations being reorganized. See Note 2—Goodwill, Customer Relationships and Other Intangible Assets for additional information. Pension and Post-Retirement Benefits We recognize the funded status of our defined benefit and post-retirement plans as an asset or a liability on our consolidated balance sheet. Each year's actuarial gains or losses are a component of our other comprehensive (loss) income, which is then included in our accumulated other comprehensive loss. Pension and post-retirement benefit expenses are recognized over the period in which the employee renders service and becomes eligible to receive benefits. We make significant assumptions (including the discount rate, expected rate of return on plan assets, mortality and health care trend rates) in computing the pension and post-retirement benefits expense and obligations. See Note 7—Employee Benefits for additional information. Foreign Currency Our results of operations include foreign subsidiaries, which are translated from the applicable functional currency to the United States Dollar using the average exchange rates during the reporting period, while assets and liabilities are translated at the reporting date. We include gains or losses from foreign currency remeasurement in other income, net in our consolidated statements of operations. Certain non-U.S. subsidiaries designate the local currency as their functional currency, and we record the translation of their assets and liabilities into U.S. dollars at the balance sheet date as translation adjustments and include them as a component of accumulated other comprehensive loss in our consolidated balance sheets. Common Stock At December 31, 2014, we had 4 million unissued shares of CenturyLink common stock reserved for acquisitions. In addition, we had 27 million shares authorized for future issuance under our equity incentive plans. Preferred stock Holders of outstanding CenturyLink preferred stock are entitled to receive cumulative dividends, receive preferential distributions equal to $25 per share plus unpaid dividends upon CenturyLink's liquidation and vote as a single class with the holders of common stock. Dividends We pay dividends out of retained earnings to the extent we have retained earnings on the date the dividend is declared. If the dividend is in excess of our retained earnings on the declaration date, then the excess is drawn from our additional paid-in capital. Recent Accounting Pronouncements On May 28, 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update 2014-09, “Revenue from Contracts with Customers” (“ASU 2014-09” or “new standard”). The new standard is effective for annual and interim periods beginning January 1, 2017, and early adoption is prohibited. ASU 2014-09 may be adopted by applying the provisions of the new standard on a retrospective basis to the periods included in the financial statements or on a modified retrospective basis which would result in the recognition of a cumulative effect of adopting ASU 2014-09 in the first quarter of 2017. We have not yet decided which implementation method we will adopt. The new standard replaces virtually all existing generally accepted accounting principles (“GAAP”) on revenue recognition and replaces them with a principles-based approach for determining revenue recognition using a new five step model. The core principle of ASU 2014-09 is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. ASU 2014-09 also includes new accounting principles related to the deferral and amortization of contract acquisition and fulfillment costs. We currently do not defer any contract acquisition costs and defer contract fulfillment costs only up to the extent of any revenue deferred. We are studying the new standard and are in the early stages of assessing the impact the new standard will have on us and our consolidated financial statements. We cannot, however, provide any estimate of the impact of adopting the new standard at this time. Out-of-Period Adjustments During the year ended December 31, 2012, we discovered and corrected an error that resulted in an overstatement of depreciation expense in 2011. We evaluated the error considering both quantitative and qualitative factors and concluded that the error was immaterial to our previously issued and current period consolidated financial statements. Therefore, we recognized a $30 million reduction in depreciation expense during the year ended December 31, 2012. The correction of the error resulted in an increase in net income of $19 million, or approximately $0.03 per basic and diluted common share, for the year ended December 31, 2012.

Basis of Presentation and Summary of Significant Accounting Policies

Basis of Presentation

We are an integrated communications company engaged primarily in providing an array of communications services to our residential, business, governmental and wholesale customers. Our communications services include local and long-distance, broadband, private line (including special access), Multi-Protocol Label Switching ("MPLS"), data integration, managed hosting (including cloud hosting), colocation, Ethernet, network access, public access, wireless, video and other ancillary services.

The accompanying consolidated financial statements include our accounts and the accounts of our subsidiaries. Intercompany amounts and transactions with our consolidated subsidiaries have been eliminated.

To simplify the overall presentation of our consolidated financial statements, we report immaterial amounts attributable to noncontrolling interests in certain of our subsidiaries as follows: (i) income attributable to noncontrolling interests in other income (expense), (ii) equity attributable to noncontrolling interests in additional paid-in capital and (iii) cash flows attributable to noncontrolling interests in other, net financing activities.

We reclassified certain prior period amounts to conform to the current period presentation, including the categorization of our revenues and our segment reporting. See Note 12—Segment Information for additional information. These changes had no impact on total revenues, total operating expenses or net income (loss) for any period.

In January 2013, we sold $43 million of our wireless spectrum assets held for sale. The sale resulted in a gain of $32 million, which is recorded as other income on our consolidated statements of operations.

Changes in Estimates

As a result of our annual reviews to evaluate the reasonableness of the depreciable lives for our property, plant and equipment, effective January 2014, we changed the estimates of the remaining economic lives of certain switch and circuit network equipment. These changes resulted in a net increase in depreciation expense of approximately $78 million for the year ended December 31, 2014. This net increase in depreciation expense, net of tax, reduced consolidated net income by approximately $48 million, or $0.08 per basic and diluted common share, for the year ended December 31, 2014.

Additionally, during the third quarter of 2014, we developed a plan to migrate customers from one of our networks to another between the fourth quarter of 2014 through the fourth quarter of 2015. As a result, we implemented changes in estimates that reduced the remaining economic lives of certain network assets. These changes increased depreciation expense of approximately $12 million for the year ended December 31, 2014 and is expected to increase depreciation expense by approximately $48 million for 2015. The increase in depreciation expense, net of tax, reduced consolidated net income by approximately $7 million, or $0.01 per basic and diluted common share, for the year ended December 31, 2014.

During the fourth quarter 2013, we changed the estimates of the remaining economic lives of certain intangible assets, specifically, the Savvis trade name, which is no longer being utilized, and certain Savvis cloud software, which has been replaced by cloud software acquired through our more recent acquisitions. These changes resulted in an increase in amortization expense of approximately $23 million for the year ended December 31, 2014. This increase in amortization expense, net of tax, reduced consolidated net income by approximately $14 million, or $0.02 per basic and diluted common share, for the year ended December 31, 2014. As of December 31, 2014, the Savvis trade name and the Savvis cloud software were fully amortized.

Summary of Significant Accounting Policies

Use of Estimates

Our consolidated financial statements are prepared in accordance with U.S. generally accepted accounting principles. These accounting principles require us to make certain estimates, judgments and assumptions. We believe that the estimates, judgments and assumptions we make when accounting for items and matters such as, but not limited to, investments, long-term contracts, customer retention patterns, allowance for doubtful accounts, depreciation, amortization, asset valuations, internal labor capitalization rates, recoverability of assets (including deferred tax assets), impairment assessments, pension, post-retirement and other post-employment benefits, taxes, certain liabilities and other provisions and contingencies are reasonable, based on information available at the time they were made. These estimates, judgments and assumptions can affect the reported amounts of assets, liabilities and components of stockholders' equity as of the dates of the consolidated balance sheets, as well as the reported amounts of revenues, expenses and components of cash flows during the periods presented in our consolidated statements of operations, our consolidated statements of comprehensive (loss) income and our consolidated statements of cash flows. We also make estimates in our assessments of potential losses in relation to threatened or pending tax and legal matters. See Note 11—Income Taxes and Note 14—Commitments and Contingencies for additional information.

For matters not related to income taxes, if a loss is considered probable and the amount can be reasonably estimated, we recognize an expense for the estimated loss. If we have the potential to recover a portion of the estimated loss from a third party, we make a separate assessment of recoverability and reduce the estimated loss if recovery is also deemed probable.

For matters related to income taxes, if we determine that the impact of an uncertain tax position is more likely than not to be sustained upon audit by the relevant taxing authority, then we recognize a benefit for the largest amount that is more likely than not to be sustained. No portion of an uncertain tax position will be recognized if the position has less than a 50% likelihood of being sustained. Interest is recognized on the amount of unrecognized benefit from uncertain tax positions.

For all of these and other matters, actual results could differ from our estimates.

Revenue Recognition

We recognize revenue for services when the related services are provided. Recognition of certain payments received in advance of services being provided is deferred until the service is provided. These advance payments include activation and installation charges, which we recognize as revenue over the expected customer relationship period, which ranges from eighteen months to over ten years depending on the service. We also defer costs for customer activations and installations. The deferral of customer activation and installation costs is limited to the amount of revenue deferred on advance payments. Costs in excess of advance payments are recorded as expense in the period such costs are incurred. Expected customer relationship periods are estimated using historical experience. Termination fees or other fees on existing contracts that are negotiated in conjunction with new contracts are deferred and recognized over the new contract term.

We offer bundle discounts to our customers who receive certain groupings of services. These bundle discounts are recognized concurrently with the associated revenue and are allocated to the various services in the bundled offering based on the estimated selling price of services included in each bundled combination.

Customer arrangements that include both equipment and services are evaluated to determine whether the elements are separable. If the elements are deemed separable and separate earnings processes exist, the revenue associated with the customer arrangement is allocated to each element based on the relative estimated selling price of the separate elements. We have estimated the selling prices of each element by reference to vendor-specific objective evidence of selling prices when the elements are sold separately. The revenue associated with each element is then recognized as earned. For example, if we receive an advance payment when we sell equipment and continuing service together, we immediately recognize as revenue the amount allocated to the equipment as long as all the conditions for revenue recognition have been satisfied. The portion of the advance payment allocated to the service based upon its relative selling price is recognized ratably over the longer of the contractual period or the expected customer relationship period.

We periodically transfer optical capacity assets on our network to other telecommunications service carriers. These transactions are structured as indefeasible rights of use, commonly referred to as IRUs, which are the exclusive right to use a specified amount of capacity or fiber for a specified term, typically 20 years. We account for the cash consideration received on transfers of optical capacity assets and on all of the other elements deliverable under an IRU, as revenue ratably over the term of the agreement. We have not recognized revenue on any contemporaneous exchanges of our optical capacity assets for other optical capacity assets.

In connection with offering products and services provided by third-party vendors, we review the relationship between us, the vendor and the end customer to assess whether revenue should be reported on a gross or net basis. In assessing whether revenue should be reported on a gross or net basis, we consider whether we act as a principal in the transaction, take title to the products, have risk and rewards of ownership or act as an agent or broker. Based on our agreements with DIRECTV and Verizon Wireless, we offer these services through sales agency relationships which are reported on a net basis.

For our hosting operations, we have service level commitments pursuant to contracts with certain of our clients. To the extent that such service levels are not achieved or are otherwise disputed due to performance or service issues or other service interruptions or conditions, we will estimate the amount of credits to be issued and record a reduction to revenues, with a corresponding increase in the credit reserve.

USF, Gross Receipts Taxes and Other Surcharges

In determining whether to include in our revenues and expenses the taxes and surcharges collected from customers and remitted to government authorities, including USF charges, sales, use, value added and some excise taxes, we assess, among other things, whether we are the primary obligor or principal taxpayer for the taxes assessed in each jurisdiction where we do business. In jurisdictions where we determine that we are the principal taxpayer, we record the surcharges on a gross basis and include them in our revenues and costs of services and products. In jurisdictions where we determine that we are merely a collection agent for the government authority, we record the taxes on a net basis and do not include them in our revenues and costs of services and products.

Advertising Costs

Costs related to advertising are expensed as incurred and included in selling, general and administrative expenses in our consolidated statements of operations. Our advertising expense was $214 million, $210 million and $189 million for the years ended December 31, 2014, 2013 and 2012, respectively.

Legal Costs

In the normal course of our business, we incur costs to hire and retain external legal counsel to advise us on regulatory, litigation and other matters. We expense these costs as the related services are received.

Income Taxes

We file a consolidated federal income tax return with our eligible subsidiaries. The provision for income taxes consists of an amount for taxes currently payable, an amount for tax consequences deferred to future periods, adjustments to our liabilities for uncertain tax positions and amortization of investment tax credits. We record deferred income tax assets and liabilities reflecting future tax consequences attributable to tax net operating losses ("NOLs"), tax credit carryforwards and differences between the financial statement carrying value of assets and liabilities and the tax bases of those assets and liabilities. Deferred taxes are computed using enacted tax rates expected to apply in the year in which the differences are expected to affect taxable income. The effect on deferred income tax assets and liabilities of a change in tax rate is recognized in earnings in the period that includes the enactment date.

We establish valuation allowances when necessary to reduce deferred income tax assets to the amounts that we believe are more likely than not to be recovered. A significant portion of our net deferred tax assets relate to tax benefits attributable to NOLs. Each quarter we evaluate the need to retain all or a portion of the valuation allowance on our deferred tax assets. See Note 11—Income Taxes for additional information.

Cash and Cash Equivalents

Cash and cash equivalents include highly liquid investments that are readily convertible into cash and are not subject to significant risk from fluctuations in interest rates. As a result, the value at which cash and cash equivalents are reported in our consolidated financial statements approximates their fair value. In evaluating investments for classification as cash equivalents, we require that individual securities have original maturities of ninety days or less and that individual investment funds have dollar-weighted average maturities of ninety days or less. To preserve capital and maintain liquidity, we invest with financial institutions we deem to be of sound financial condition and in high quality and relatively risk-free investment products. Our cash investment policy limits the concentration of investments with specific financial institutions or among certain products and includes criteria related to credit worthiness of any particular financial institution.

Book overdrafts occur when checks have been issued but have not been presented to our controlled disbursement bank accounts for payment. Disbursement bank accounts allow us to delay funding of issued checks until the checks are presented for payment. Until the issued checks are presented for payment, the book overdrafts are included in accounts payable on our consolidated balance sheet. This activity is included in the operating activities section in our consolidated statements of cash flows.

Accounts Receivable and Allowance for Doubtful Accounts

Accounts receivable are recognized based upon the amount due from customers for the services provided or at cost for purchased and other receivables less an allowance for doubtful accounts. The allowance for doubtful accounts receivable reflects our best estimate of probable losses inherent in our receivable portfolio determined on the basis of historical experience, specific allowances for known troubled accounts and other currently available evidence. We generally consider our accounts past due if they are outstanding over 30 days. Our collection process varies by the customer segment, amount of the receivable, and our evaluation of the customer's credit risk. Our past due accounts are written off against our allowance for doubtful accounts when collection is considered to be not probable. Any recoveries of accounts previously written off are generally recognized as a reduction in bad debt expense in the period received. The carrying value of accounts receivable net of the allowance for doubtful accounts approximates fair value.

Property, Plant and Equipment

Property, plant and equipment acquired in connection with our acquisitions was recorded based on its estimated fair value as of its acquisition date plus the estimated value of any associated legally or contractually required retirement obligations. Purchased and constructed property, plant and equipment is recorded at cost, plus the estimated value of any associated legally or contractually required retirement obligations. Property, plant and equipment is depreciated primarily using the straight-line group method. Under the straight-line group method, assets dedicated to providing telecommunications services (which comprise the majority of our property, plant and equipment) that have similar physical characteristics, use and expected useful lives are pooled for purposes of depreciation and tracking. The equal life group procedure is used to establish each pool's average remaining useful life. Generally, under the straight-line group method, when an asset is sold or retired in the course of normal business activities, the cost is deducted from property, plant and equipment and charged to accumulated depreciation without recognition of a gain or loss. A gain or loss is recognized in our consolidated statements of operations only if a disposal is abnormal or unusual. Leasehold improvements are amortized over the shorter of the useful lives of the assets or the expected lease term. Expenditures for maintenance and repairs are expensed as incurred. Interest is capitalized during the construction phase of network and other internal-use capital projects. Employee-related costs for construction of network and other internal use assets are also capitalized during the construction phase. Property, plant and equipment supplies used internally are carried at average cost, except for significant individual items for which cost is based on specific identification.

We perform annual internal reviews to evaluate the reasonableness of the depreciable lives for our property, plant and equipment. Our reviews utilize models that take into account actual usage, physical wear and tear, replacement history, assumptions about technology evolution and, in certain instances, actuarially determined probabilities to estimate the remaining useful life of our asset base. Our remaining useful life assessments anticipate the loss in service value of assets that may precede the physical retirement. Assets shared among many customers may lose service value as those customers leave the network. However, the asset is not retired until all customers no longer utilize the asset.

We have asset retirement obligations associated with the legally or contractually required removal of a limited group of property, plant and equipment assets from leased properties and the disposal of certain hazardous materials present in our owned properties. When an asset retirement obligation is identified, usually in association with the acquisition of the asset, we record the fair value of the obligation as a liability. The fair value of the obligation is also capitalized as property, plant and equipment and then amortized over the estimated remaining useful life of the associated asset. Where the removal obligation is not legally binding, the net cost to remove assets is expensed in the period in which the costs are actually incurred.

We review long-lived tangible assets for impairment whenever facts and circumstances indicate that the carrying amounts of the assets may not be recoverable. For assessment purposes, long-lived assets are grouped with other assets and liabilities at the lowest level for which identifiable cash flows are largely independent of the cash flows of other assets and liabilities, absent a material change in operations. An impairment loss is recognized only if the carrying amount of the asset group is not recoverable and exceeds its fair value. Recoverability of the asset group to be held and used is assessed by comparing the carrying amount of the asset group to the estimated undiscounted future net cash flows expected to be generated by the asset group. If the asset group's carrying value is not recoverable, an impairment charge is recognized for the amount by which the carrying amount of the asset group exceeds its fair value. We determine fair values by using a combination of comparable market values and discounted cash flows, as appropriate.

Goodwill, Customer Relationships and Other Intangible Assets

Intangible assets arising from business combinations, such as goodwill, customer relationships, capitalized software, trademarks and trade names, are initially recorded at estimated fair value. We amortize customer relationships primarily over an estimated life of 10 to 15 years, using either the sum-of-the-years-digits or the straight-line methods, depending on the type of customer. We amortize capitalized software using the straight-line method over estimated lives ranging up to 7 years, except for approximately $237 million of our capitalized software costs, which represents costs to develop an integrated billing and customer care system which is amortized using the straight-line method over a 20 year period. We amortize our other intangible assets predominantly using the sum-of-the-years-digits method over an estimated life of 4 years. Other intangible assets not arising from business combinations are initially recorded at cost. Where there are no legal, regulatory, contractual or other factors that would reasonably limit the useful life of an intangible asset, we classify the intangible asset as indefinite-lived and such intangible assets are not amortized.

Internally used software, whether purchased or developed by us, is capitalized and amortized using the straight-line method over its estimated useful life. We have capitalized certain costs associated with software such as costs of employees devoting time to the projects and external direct costs for materials and services. Costs associated with software to be used for internal purposes are expensed until the point at which the project has reached the development stage. Subsequent additions, modifications or upgrades to internal-use software are capitalized only to the extent that they allow the software to perform a task it previously did not perform. Software maintenance, data conversion and training costs are expensed in the period in which they are incurred. We review the remaining economic lives of our capitalized software annually. Capitalized software is included in other intangible assets, net, in our consolidated balance sheets.

Our long-lived intangible assets, other than goodwill, with indefinite lives are assessed for impairment annually, or, under certain circumstances, more frequently, such as when events or circumstances indicate there may be an impairment. These assets are carried at the estimated fair value at the time of acquisition and assets not acquired in acquisitions are recorded at historical cost. However, if their estimated fair value is less than the carrying amount, other indefinite-lived intangible assets are reduced to their estimated fair value through an impairment charge to our consolidated statements of operations.

We annually review the estimated lives and methods used to amortize our other intangible assets. The actual amounts of amortization expense may differ materially from our estimates, depending on the results of our annual review.

We are required to assess goodwill for impairment at least annually, or more frequently if events or a change in circumstances indicate that an impairment may have occurred. We are required to write-down the value of goodwill in periods in which the recorded amount of goodwill exceeds the implied fair value of goodwill. Our reporting units are not discrete legal entities with discrete financial statements. Our assets and liabilities are employed in and relate to the operations of multiple reporting units. Therefore, the equity carrying value and future cash flows must be estimated each time a goodwill impairment assessment is performed on a reporting unit. As a result, our assets, liabilities and cash flows are assigned to reporting units using reasonable and consistent allocation methodologies. Certain estimates, judgments and assumptions are required to perform these assignments. We believe these estimates, judgments and assumptions to be reasonable, but changes in many of these can significantly affect each reporting unit's equity carrying value and future cash flows utilized for our goodwill impairment assessment.

During the fourth quarter of 2013, we elected to change the date of our annual assessment of goodwill impairment from September 30 to October 31. This is a change in method of applying an accounting principle which management believes is a preferable alternative as the new date of the assessment is more closely aligned with our strategic planning process. The change in the assessment date did not delay, accelerate or avoid a potential impairment charge in 2013. We performed our annual goodwill impairment assessment at September 30, 2013, prior to the change in our annual assessment date. We then performed a qualitative assessment of our goodwill as of October 31, 2013 and concluded that our goodwill for consumer, wholesale and business reporting units was not impaired and our goodwill for hosting reporting unit was not further impaired as of that date.

We are required to reassign goodwill to reporting units each time we reorganize our internal reporting structure which causes a change in the composition of our reporting units. Goodwill is reassigned to the reporting units using a relative fair value approach. We utilize the earnings before interest, taxes, depreciation and amortization as our allocation methodology as it represents a reasonable proxy for the fair value of the operations being reorganized.

See Note 2—Goodwill, Customer Relationships and Other Intangible Assets for additional information.

Pension and Post-Retirement Benefits

We recognize the funded status of our defined benefit and post-retirement plans as an asset or a liability on our consolidated balance sheet. Each year's actuarial gains or losses are a component of our other comprehensive (loss) income, which is then included in our accumulated other comprehensive loss. Pension and post-retirement benefit expenses are recognized over the period in which the employee renders service and becomes eligible to receive benefits. We make significant assumptions (including the discount rate, expected rate of return on plan assets, mortality and health care trend rates) in computing the pension and post-retirement benefits expense and obligations. See Note 7—Employee Benefits for additional information.

Foreign Currency

Our results of operations include foreign subsidiaries, which are translated from the applicable functional currency to the United States Dollar using the average exchange rates during the reporting period, while assets and liabilities are translated at the reporting date. We include gains or losses from foreign currency remeasurement in other income, net in our consolidated statements of operations. Certain non-U.S. subsidiaries designate the local currency as their functional currency, and we record the translation of their assets and liabilities into U.S. dollars at the balance sheet date as translation adjustments and include them as a component of accumulated other comprehensive loss in our consolidated balance sheets.

Common Stock

At December 31, 2014, we had 4 million unissued shares of CenturyLink common stock reserved for acquisitions. In addition, we had 27 million shares authorized for future issuance under our equity incentive plans.

Preferred stock

Holders of outstanding CenturyLink preferred stock are entitled to receive cumulative dividends, receive preferential distributions equal to $25 per share plus unpaid dividends upon CenturyLink's liquidation and vote as a single class with the holders of common stock.

Dividends

We pay dividends out of retained earnings to the extent we have retained earnings on the date the dividend is declared. If the dividend is in excess of our retained earnings on the declaration date, then the excess is drawn from our additional paid-in capital.

Recent Accounting Pronouncements

On May 28, 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update 2014-09, “Revenue from Contracts with Customers” (“ASU 2014-09” or “new standard”). The new standard is effective for annual and interim periods beginning January 1, 2017, and early adoption is prohibited. ASU 2014-09 may be adopted by applying the provisions of the new standard on a retrospective basis to the periods included in the financial statements or on a modified retrospective basis which would result in the recognition of a cumulative effect of adopting ASU 2014-09 in the first quarter of 2017. We have not yet decided which implementation method we will adopt.

The new standard replaces virtually all existing generally accepted accounting principles (“GAAP”) on revenue recognition and replaces them with a principles-based approach for determining revenue recognition using a new five step model. The core principle of ASU 2014-09 is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. ASU 2014-09 also includes new accounting principles related to the deferral and amortization of contract acquisition and fulfillment costs. We currently do not defer any contract acquisition costs and defer contract fulfillment costs only up to the extent of any revenue deferred.

We are studying the new standard and are in the early stages of assessing the impact the new standard will have on us and our consolidated financial statements. We cannot, however, provide any estimate of the impact of adopting the new standard at this time.

Out-of-Period Adjustments

During the year ended December 31, 2012, we discovered and corrected an error that resulted in an overstatement of depreciation expense in 2011. We evaluated the error considering both quantitative and qualitative factors and concluded that the error was immaterial to our previously issued and current period consolidated financial statements. Therefore, we recognized a $30 million reduction in depreciation expense during the year ended December 31, 2012. The correction of the error resulted in an increase in net income of $19 million, or approximately $0.03 per basic and diluted common share, for the year ended December 31, 2012.