Summary of Significant Accounting Policies (Policies)	9 Months Ended
Sep. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Principles of Consolidation	These unaudited condensed consolidated financial statements (the “financial statements”) include the accounts of Northrop Grumman Corporation and its subsidiaries and joint ventures or other investments for which we consolidate the financial results (herein referred to as “Northrop Grumman,” the “company,” “we,” “us,” or “our”). Intercompany accounts, transactions and profits are eliminated in consolidation. Investments in equity securities and joint ventures where the company has significant influence, but not control, are accounted for using the equity method.
Basis of Presentation	These financial statements are prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP” or “FAS”) and in accordance with the rules of the Securities and Exchange Commission (SEC) for interim reporting. The financial statements include adjustments of a normal recurring nature considered necessary by management for a fair presentation of the company’s unaudited condensed consolidated financial position, results of operations and cash flows. Effective January 1, 2020, the company reorganized its operating sectors to better align the company’s broad portfolio to serve its customers’ needs. The four new sectors, which also comprise our reportable segments, are Aeronautics Systems, Defense Systems, Mission Systems and Space Systems. Beginning in the second quarter of 2020, the company no longer considers certain unallowable costs and environmental matters that are principally managed at the corporate office as part of management’s evaluation of segment operating performance. As a result, certain unallowable compensation and other costs, which were previously included in segment operating results, are now reported in Unallocated corporate expense within operating income. In addition, certain accrued and deferred costs, as well as unallowable costs, if any, associated with certain environmental matters that were previously reflected in segment assets and operating results are now reflected in corporate assets and Unallocated corporate expense within operating income. The impact of these changes are reflected in the amounts in this Form 10-Q. See Part II, Item 5 in the Quarterly Report on Form 10-Q for the quarter ended June 30, 2020 and Note 9 for further information regarding the impact of these changes on the company’s prior period segment operating income. The results reported in these financial statements are not necessarily indicative of results that may be expected for the entire year. These financial statements should be read in conjunction with the information contained in the company’s 2019 Annual Report on Form 10-K, the Form 8-K that we filed with the SEC on April 29, 2020, which recasts the disclosures in certain portions of the 2019 Annual Report on Form 10-K to reflect changes in the company’s reportable segments, and the Quarterly Reports on Form 10-Q for the quarters ended March 31, 2020 and June 30, 2020.
Fiscal Period Policy	The quarterly information is labeled using a calendar convention; that is, first quarter is consistently labeled as ending on March 31, second quarter as ending on June 30 and third quarter as ending on September 30. It is the company’s long-standing practice to establish actual interim closing dates using a “fiscal” calendar, in which we close our books on a Friday near these quarter-end dates in order to normalize the potentially disruptive effects of quarterly closings on business processes. This practice is only used at interim periods within a reporting year.
Accounting Estimates	Preparation of the financial statements requires management to make estimates and judgments that affect the reported amounts of assets and liabilities and the disclosure of contingencies at the date of the financial statements, as well as the reported amounts of sales and expenses during the reporting period. Estimates have been prepared using the most current and best available information; however, actual results could differ materially from those estimates.
Revenue from Contract with Customer	Revenue Recognition The majority of our sales are derived from long-term contracts with the U.S. government for the development or production of goods, the provision of services, or a combination of both. We recognize revenue as control is transferred to the customer, either over time or at a point in time. For most of our contracts, control is effectively transferred during the period of performance, so we generally recognize revenue over time using the cost-to-cost method (cost incurred relative to total cost estimated at completion). The company believes this represents the most appropriate measurement towards satisfaction of our performance obligations. Revenue for contracts in which the control of goods produced does not transfer until delivery to the customer is recognized at a point in time (i.e., typically upon delivery). Contract Estimates Use of the cost-to-cost method requires us to make reasonably dependable estimates regarding the revenue and cost associated with the design, manufacture and delivery of our products and services. The company estimates profit on these contracts as the difference between total estimated sales and total estimated cost at completion and recognizes that profit as costs are incurred. Significant judgment is used to estimate total sales and cost at completion. Contract sales may include estimates of variable consideration, including cost or performance incentives (such as award and incentive fees), contract claims and requests for equitable adjustment (REAs). Variable consideration is included in total estimated sales to the extent it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is subsequently resolved. We estimate variable consideration as the most likely amount to which we expect to be entitled. We recognize changes in estimated contract sales or costs and the resulting changes in contract profit on a cumulative basis. Cumulative EAC adjustments represent the cumulative effect of the changes on current and prior periods; sales and operating margins in future periods are recognized as if the revised estimates had been used since contract inception. If it is determined that a loss is expected to result on an individual performance obligation, the entire amount of the estimable future loss, including an allocation of general and administrative (G&A) expense, is charged against income in the period the loss is identified. Contract Assets and Liabilities For each of the company’s contracts, the timing of revenue recognition, customer billings, and cash collections results in a net contract asset or liability at the end of each reporting period. Contract assets are equivalent to and reflected as Unbilled receivables in the unaudited condensed consolidated statements of financial position and are primarily related to long-term contracts where revenue recognized under the cost-to-cost method exceeds amounts billed to customers. Contract liabilities are equivalent to and reflected as Advance payments and billings in excess of costs incurred in the unaudited condensed consolidated statements of financial position.
Earnings Per Share	Diluted earnings per share include the dilutive effect of awards granted to employees under stock-based compensation plans. We calculate basic earnings per share by dividing net earnings by the weighted-average number of shares of common stock outstanding during each period.
Investments in Marketable Securities	The company holds a portfolio of marketable securities to partially fund non-qualified employee benefit plans. A portion of these securities are held in common/collective trust funds and are measured at fair value using net asset value (NAV) per share as a practical expedient; and therefore are not required to be categorized in the fair value hierarchy table
Derivative Financial Instruments and Hedging Activities	Where model-derived valuations are appropriate, the company utilizes the income approach to determine the fair value and uses the applicable London Interbank Offered Rate (LIBOR) swap rates.
Fair Value of Long-term Debt	We calculated the fair value of long-term debt using Level 2 inputs, based on interest rates available for debt with terms and maturities similar to the company’s existing debt arrangements.
U.S. Government Cost Claims	From time to time, the company is advised of claims by the U.S. government concerning certain potential disallowed costs, plus, at times, penalties and interest. When such findings are presented, the company and U.S. government representatives engage in discussions to enable the company to evaluate the merits of these claims, as well as to assess the amounts being claimed. Where appropriate, provisions are made to reflect the company’s estimated exposure for such potential disallowed costs. Such provisions are reviewed periodically using the most recent information available.
Pension and Other Postretirement Plans	We fund our defined benefit pension plans annually in a manner consistent with the Employee Retirement Income Security Act of 1974, as amended by the Pension Protection Act of 2006

Summary of Significant Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2020

Organization, Consolidation and Presentation of Financial Statements [Abstract]

These unaudited condensed consolidated financial statements (the “financial statements”) include the accounts of Northrop Grumman Corporation and its subsidiaries and joint ventures or other investments for which we consolidate the financial results (herein referred to as “Northrop Grumman,” the “company,” “we,” “us,” or “our”). Intercompany accounts, transactions and profits are eliminated in consolidation. Investments in equity securities and joint ventures where the company has significant influence, but not control, are accounted for using the equity method.

Basis of Presentation

These financial statements are prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP” or “FAS”) and in accordance with the rules of the Securities and Exchange Commission (SEC) for interim reporting. The financial statements include adjustments of a normal recurring nature considered necessary by management for a fair presentation of the company’s unaudited condensed consolidated financial position, results of operations and cash flows.

Effective January 1, 2020, the company reorganized its operating sectors to better align the company’s broad portfolio to serve its customers’ needs. The four new sectors, which also comprise our reportable segments, are Aeronautics Systems, Defense Systems, Mission Systems and Space Systems.

Beginning in the second quarter of 2020, the company no longer considers certain unallowable costs and environmental matters that are principally managed at the corporate office as part of management’s evaluation of segment operating performance. As a result, certain unallowable compensation and other costs, which were previously included in segment operating results, are now reported in Unallocated corporate expense within operating income. In addition, certain accrued and deferred costs, as well as unallowable costs, if any, associated with certain environmental matters that were previously reflected in segment assets and operating results are now reflected in corporate assets and Unallocated corporate expense within operating income. The impact of these changes are reflected in the amounts in this Form 10-Q. See Part II, Item 5 in the Quarterly Report on Form 10-Q for the quarter ended June 30, 2020 and Note 9 for further information regarding the impact of these changes on the company’s prior period segment operating income.

The results reported in these financial statements are not necessarily indicative of results that may be expected for the entire year. These financial statements should be read in conjunction with the information contained in the company’s 2019 Annual Report on Form 10-K, the Form 8-K that we filed with the SEC on April 29, 2020, which recasts the disclosures in certain portions of the 2019 Annual Report on Form 10-K to reflect changes in the company’s reportable segments, and the Quarterly Reports on Form 10-Q for the quarters ended March 31, 2020 and June 30, 2020.

Fiscal Period Policy

The quarterly information is labeled using a calendar convention; that is, first quarter is consistently labeled as ending on March 31, second quarter as ending on June 30 and third quarter as ending on September 30. It is the company’s long-standing practice to establish actual interim closing dates using a “fiscal” calendar, in which we close our books on a Friday near these quarter-end dates in order to normalize the potentially disruptive effects of quarterly closings on business processes. This practice is only used at interim periods within a reporting year.

Accounting Estimates

Preparation of the financial statements requires management to make estimates and judgments that affect the reported amounts of assets and liabilities and the disclosure of contingencies at the date of the financial statements, as well as the reported amounts of sales and expenses during the reporting period. Estimates have been prepared using the most current and best available information; however, actual results could differ materially from those estimates.

Revenue from Contract with Customer

Revenue Recognition

The majority of our sales are derived from long-term contracts with the U.S. government for the development or production of goods, the provision of services, or a combination of both. We recognize revenue as control is transferred to the customer, either over time or at a point in time. For most of our contracts, control is effectively transferred during the period of performance, so we generally recognize revenue over time using the cost-to-cost method (cost incurred relative to total cost estimated at completion). The company believes this represents the most appropriate measurement towards satisfaction of our performance obligations. Revenue for contracts in which the control of goods produced does not transfer until delivery to the customer is recognized at a point in time (i.e., typically upon delivery).

Contract Estimates

Use of the cost-to-cost method requires us to make reasonably dependable estimates regarding the revenue and cost associated with the design, manufacture and delivery of our products and services. The company estimates profit on these contracts as the difference between total estimated sales and total estimated cost at completion and recognizes that profit as costs are incurred. Significant judgment is used to estimate total sales and cost at completion.

Contract sales may include estimates of variable consideration, including cost or performance incentives (such as award and incentive fees), contract claims and requests for equitable adjustment (REAs). Variable consideration is included in total estimated sales to the extent it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is subsequently resolved. We estimate variable consideration as the most likely amount to which we expect to be entitled.

We recognize changes in estimated contract sales or costs and the resulting changes in contract profit on a cumulative basis. Cumulative EAC adjustments represent the cumulative effect of the changes on current and prior periods; sales and operating margins in future periods are recognized as if the revised estimates had been used since contract inception. If it is determined that a loss is expected to result on an individual performance obligation, the entire amount of the estimable future loss, including an allocation of general and administrative (G&A) expense, is charged against income in the period the loss is identified.

Contract Assets and Liabilities

For each of the company’s contracts, the timing of revenue recognition, customer billings, and cash collections results in a net contract asset or liability at the end of each reporting period. Contract assets are equivalent to and reflected as Unbilled receivables in the unaudited condensed consolidated statements of financial position and are primarily related to long-term contracts where revenue recognized under the cost-to-cost method exceeds amounts billed to customers. Contract liabilities are equivalent to and reflected as Advance payments and billings in excess of costs incurred in the unaudited condensed consolidated statements of financial position.

Earnings Per Share

Diluted earnings per share include the dilutive effect of awards granted to employees under stock-based compensation plans.

We calculate basic earnings per share by dividing net earnings by the weighted-average number of shares of common stock outstanding during each period.

Investments in Marketable Securities

The company holds a portfolio of marketable securities to partially fund non-qualified employee benefit plans. A portion of these securities are held in common/collective trust funds and are measured at fair value using net asset value (NAV) per share as a practical expedient; and therefore are not required to be categorized in the fair value hierarchy table

Derivative Financial Instruments and Hedging Activities

Where model-derived valuations are appropriate, the company utilizes the income approach to determine the fair value and uses the applicable London Interbank Offered Rate (LIBOR) swap rates.

Fair Value of Long-term Debt

We calculated the fair value of long-term debt using Level 2 inputs, based on interest rates available for debt with terms and maturities similar to the company’s existing debt arrangements.

U.S. Government Cost Claims

From time to time, the company is advised of claims by the U.S. government concerning certain potential disallowed costs, plus, at times, penalties and interest. When such findings are presented, the company and U.S. government representatives engage in discussions to enable the company to evaluate the merits of these claims, as well as to assess the amounts being claimed. Where appropriate, provisions are made to reflect the company’s estimated exposure for such potential disallowed costs. Such provisions are reviewed periodically using the most recent information available.

Pension and Other Postretirement Plans

We fund our defined benefit pension plans annually in a manner consistent with the Employee Retirement Income Security Act of 1974, as amended by the Pension Protection Act of 2006