Basis of Presentation (Policies)	9 Months Ended
Basis of Presentation (Policies)	Sep. 25, 2015
Accounting Policies [Abstract]
Principles of Consolidation and Reporting	*Principles of Consolidation and Reporting* The accompanying financial statements comprise the consolidated financial statements of L-3 Holdings and L-3 Communications. L-3 Holdings’ only asset is its investment in the common stock of L-3 Communications, its wholly-owned subsidiary, and its only obligations are: (1) its guarantee of borrowings under the Amended and Restated Revolving Credit Facility (Credit Facility) of L-3 Communications and (2) its guarantee of other contractual obligations of L-3 Communications and its subsidiaries. All issuances of and conversions into L-3 Holdings’ equity securities, including grants of stock options, restricted stock units and performance units by L-3 Holdings to employees and directors of L-3 Communications and its subsidiaries, have been reflected in the consolidated financial statements of L-3 Communications. As a result, the consolidated financial positions, results of operations and cash flows of L-3 Holdings and L-3 Communications are substantially the same. See Note 23 for additional information regarding the unaudited financial information of L-3 Communications and its subsidiaries. The unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (U.S. GAAP) for interim financial information and in accordance with the instructions to Form 10-Q and Article 10 of Regulation S-X of the Securities and Exchange Commission (SEC). Accordingly, they do not include all of the disclosures required by U.S. GAAP for a complete set of annual audited financial statements. The December 31, 2014 condensed consolidated balance sheet data was derived from audited financial statements, but does not include all disclosures required by U.S. GAAP. In the opinion of management, all adjustments (consisting of normal and recurring adjustments) considered necessary for a fair statement of the results for the interim periods presented have been included. The results of operations for the interim periods are not necessarily indicative of results for the full year. It is the Company’s established practice to close its books for the quarters ending March, June and September on the Friday preceding the end of the calendar quarter. The interim unaudited condensed consolidated financial statements included herein have been prepared and are labeled based on that convention. The Company closes its books for annual periods on December 31 regardless of what day it falls on. Certain reclassifications have been made to conform prior-year amounts to the current-year presentation.
Accounting Estimates	*Accounting Estimates* The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of sales and costs of sales during the reporting period. The most significant of these estimates and assumptions for L-3 relate to contract revenue, profit and loss recognition, fair values of assets acquired and liabilities assumed in business combinations, market values for inventories reported at lower of cost or market, pension and post-retirement benefit obligations, stock-based employee compensation expense, income taxes, including the valuation of deferred tax assets, litigation reserves and environmental obligations, accrued product warranty costs, and the recoverability, useful lives and valuation of recorded amounts of long-lived assets, identifiable intangible assets and goodwill. Changes in estimates are reflected in the periods during which they become known. Actual amounts will differ from these estimates and could differ materially. Sales and profits on contracts that are covered by accounting standards for construction-type and production-type contracts and federal government contractors are recognized using percentage-of-completion (POC) methods of accounting. Approximately 46% of the Company’s net sales in 2014 were accounted for under contract accounting standards, of which approximately 40% were fixed-price type contracts and approximately 6% were cost-plus type contracts. For contracts that are accounted for under contract accounting standards, sales and profits are recognized based on: (1) a POC method of accounting (fixed-price contracts), (2) allowable costs incurred plus the estimated profit on those costs (cost-plus contracts), or (3) direct labor hours expended multiplied by the contractual fixed rate per hour plus incurred costs for material (time-and-material contracts). Sales and profits on fixed-price production contracts under which units are produced and delivered in a continuous or sequential process are recorded as units are delivered based on their contractual selling prices (the “units-of-delivery” method). Sales and profits on each fixed-price production contract under which units are not produced and delivered in a continuous or sequential process, or under which a relatively few number of units are produced, are recorded based on the ratio of actual cumulative costs incurred to total estimated costs at completion of the contract, multiplied by the total estimated contract revenue, less cumulative sales recognized in prior periods (the “cost-to-cost” method). Under both POC methods of accounting, a single estimated total profit margin is used to recognize profit for each contract over its entire period of performance, which can exceed one year. Accounting for the sales and profit on these fixed-price type contracts requires the preparation of estimates of: (1) the total contract revenue, (2) the total costs at completion, which is equal to the sum of the actual incurred costs to date on the contract and the estimated costs to complete the contract’s statement of work, and (3) the measurement of progress towards completion. The estimated profit or loss at completion on a contract is equal to the difference between the total estimated contract revenue and the total estimated cost at completion. The profit recorded on a contract in any period using either the units-of-delivery method or cost-to-cost method is equal to the current estimated total profit margin multiplied by the cumulative sales recognized, less the amount of cumulative profit previously recorded for the contract. Sales and profits on cost-plus type contracts that are covered by contract accounting standards are recognized as allowable costs are incurred on the contract, at an amount equal to the allowable costs plus the estimated profit on those costs. The estimated profit on a cost-plus type contract is fixed or variable based on the contractual fee arrangement. Incentive and award fees are the primary variable fee contractual arrangement types for the Company. Incentive and award fees on cost-plus type contracts are included as an element of total estimated contract revenues and are recorded as sales when a basis exists for the reasonable prediction of performance in relation to established contractual targets and the Company is able to make reasonably dependable estimates for them. Sales and profits on time-and-material type contracts are recognized on the basis of direct labor hours expended multiplied by the contractual fixed rate per hour, plus the actual costs of materials and other direct non-labor costs. Revisions or adjustments to estimates for a contract’s revenue, estimated costs at completion and estimated profit or loss are often required as work progresses under a contract, as experience is gained, as facts and circumstances change and as new information is obtained, even though the scope of work required under the contract may not change. Revisions or adjustments may also be required if contract modifications occur. The impact of revisions in profit (loss) estimates for all types of contracts subject to POC accounting are recognized on a cumulative catch-up basis in the period in which the revisions are made. The revisions in contract estimates, if significant, can materially affect the Company’s results of operations and cash flows, as well as reduce the valuations of receivables and inventories, and in some cases result in liabilities to complete contracts in a loss position. Aggregate net changes in contract estimates amounted to increases of $52 million, or 34% of consolidated operating income (8% of segment operating income) for the year-to-date period ended September 25, 2015, and increases of $71 million, or 9% of consolidated operating income for the year-to-date period ended September 26, 2014. For a more complete discussion of these estimates and assumptions, see the Annual Report on Form 10-K for the year ended December 31, 2014.
Adoption of New Accounting Standards	In July 2015, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2015-11, to simplify the measurement of inventory. This update requires that inventory measured at first in, first out or average cost be measured at the lower of cost and net realizable value. This update is effective for interim and annual periods beginning after December 15, 2016. The Company is currently evaluating the expected impact of the adoption of this standard on its consolidated financial statements. In April 2015, the FASB issued ASU 2015-3, to simplify the presentation of debt issuance costs. This update requires that debt issuance costs be presented in the balance sheet as a direct deduction from the carrying amount of the associated debt liability, consistent with the required presentation for debt discounts. This update is effective for interim and annual periods beginning after December 15, 2015 and early adoption is permitted. The adoption of this standard will change the Company’s current practice of presenting debt issuance costs as an asset and will result in a reduction of total assets and total liabilities in an amount equal to the balance of unamortized debt issuance costs at each balance sheet date. The Company has not elected to early adopt this standard and debt issuance costs amounted to $22 million at September 25, 2015 and $27 million at December 31, 2014. In May 2014, the FASB issued ASU 2014-9, Revenue from Contracts with Customers, which will replace numerous requirements in U.S. GAAP, including industry-specific requirements, provide companies with a single revenue recognition model for recognizing revenue from contracts with customers and significantly expand the disclosure requirements for revenue arrangements. The new standard, as amended, will be effective for the Company for interim and annual reporting periods beginning on January 1, 2018, with early application permitted beginning on January 1, 2017. The two permitted transition methods under the new standard are the full retrospective method, in which case the standard would be applied to each prior reporting period presented, or the modified retrospective method, in which case the cumulative effect of applying the standard would be recognized at the date of initial application. The Company is currently evaluating the expected impact of the adoption of this standard on its consolidated financial statements and related disclosures and the transition alternatives available. As the new standard will supersede substantially all existing revenue guidance, it could impact revenue and cost recognition on substantially all of the Company’s contracts, in addition to the Company’s business processes and information technology systems. As a result, the Company’s evaluation of the impact of the standard will extend over future periods. Other accounting standard updates effective for interim and annual periods beginning after December 15, 2015 are not expected to have an impact on the Company’s financial position, results of operations or cash flows.