Nature of Operations and Significant Accounting Policies (Policies)	6 Months Ended
Jun. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	In the opinion of management, the accompanying consolidated financial statements contain all normal, recurring adjustments necessary to fairly present the consolidated financial statements and accompanying notes. Where applicable, prior year information has been reclassified to conform to the current presentation. Pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”), certain information and disclosures normally included in the notes to the annual financial statements prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) have been omitted from these interim financial statements. CSX suggests that these financial statements be read in conjunction with the audited financial statements and the notes included in CSX's most recent annual report on Form 10-K and any subsequently filed current reports on Form 8-K.
Fiscal Year	The Company's fiscal periods are based upon the calendar year. Except as otherwise specified, references to “second quarter(s)” or “six months” indicate CSX's fiscal periods ending June 30, 2020 and June 30, 2019, and references to "year-end" indicate the fiscal year ended December 31, 2019.
New Accounting Pronouncements	In June 2016, the FASB issued ASU Measurement of Credit Losses on Financial Instruments, which replaces current methods for evaluating impairment of financial instruments not measured at fair value, including trade accounts receivable and certain debt securities, with a current expected credit loss model. CSX adopted this new standard update effective January 1, 2020, and it did not have a material effect on the Company's results of operations. In August 2018, the FASB issued ASU Changes to the Disclosure Requirements for Defined Benefit Plans as part of its disclosure effectiveness initiative, which modifies the disclosure requirements for employer-sponsored defined benefit pension and other postretirement plans. This update is effective for the Company beginning January 1, 2021 and adoption of the standard is not expected to significantly impact the Company's disclosures.
Revenue Recognition	The Company generates revenue from freight billings under contracts with customers generally on a rate per carload, container or ton-basis based on length of haul and commodities carried. The Company’s performance obligation arises when it receives a bill of lading (“BOL”) to transport a customer's commodities at a negotiated price contained in a transportation services agreement or a publicly disclosed tariff rate. Once a BOL is received, a contract is formed whereby the parties are committed to perform, collectability of consideration is probable and the rights of the parties, shipping terms and conditions, and payment terms are identified. A customer may submit several BOLs for transportation services at various times throughout a service agreement term but each shipment represents a distinct service that is a separately identified performance obligation. NOTE 8. Revenues, continued The average transit time to complete a shipment is between 3 to 8 days depending on market. Payments for transportation services are normally billed once a BOL is received and are generally due within 15 days after the invoice date. The Company recognizes revenue over transit time of freight as it moves from origin to destination. Revenue for services started but not completed at the reporting date is allocated based on the relative transit time in each reporting period, with the portion allocated for services subsequent to the reporting date considered remaining performance obligations. The certain key estimates included in the recognition and measurement of revenue and related accounts receivable are as follows: •Revenue associated with shipments in transit is recognized ratably over transit time and is based on average cycle times to move commodities and products from their origin to their final destination or interchange; •Adjustments to revenue for billing corrections and billing discounts; •Adjustments to revenue for overcharge claims filed by customers, which are based on historical payments to customers for rate overcharges as a percentage of total billing; and •Incentive-based refunds to customers, which are primarily volume-related, are recorded as a reduction to revenue on the basis of the projected liability (this estimate is based on historical activity, current volume levels and forecasted future volume). Revenue related to interline transportation services that involve the services of another party, such as another railroad, is reported on a net basis. The portion of the gross amount billed to customers that is remitted by the Company to another party is not reflected as revenue. Other revenue is comprised of revenue from regional subsidiary railroads and incidental charges, including demurrage and switching. It is recorded upon completion of the service and accounts for an immaterial percentage of the Company's total revenue. Revenue from regional subsidiary railroads includes shipments by railroads that the Company does not directly operate. Demurrage represents charges assessed when freight cars are held by a customer beyond a specified period of time. Switching represents charges assessed when a railroad switches cars for a customer or another railroad. During the second quarters and six months ended 2020 and 2019, revenue recognized from performance obligations related to prior periods (for example, due to changes in transaction price), was not material. Remaining performance obligations represent the transaction price allocated to future reporting periods for freight services started but not completed at the reporting date. This includes the unearned portion of billed and unbilled amounts for cancellable freight shipments in transit. The Company expects to recognize the unearned portion of revenue for freight services in transit within one week of the reporting date.The timing of revenue recognition, billings and cash collections results in accounts receivable and customer advances and deposits (contract liabilities) on the consolidated balance sheets. Freight receivables include amounts earned, billed and unbilled, and currently due from customers for transportation-related services. Non-freight receivables include amounts billed and unbilled and currently due related to government reimbursement receivables and other non-revenue receivables. The Company maintains an allowance for credit losses to provide for the estimated amount of receivables that will not be collected. The allowance is based upon an assessment of risk characteristics, historical payment experience, and the age of outstanding receivables adjusted for forward-looking economic conditions as necessary.
Fair Value Measurements	The Financial Instruments Topic in the ASC requires disclosures about fair value of financial instruments in annual reports as well as in quarterly reports. For CSX, this statement applies to certain investments, long-term debt and interest rate derivatives. Disclosure of the fair value of pension plan assets is only required annually. Also, this rule clarifies the definition of fair value for financial reporting, establishes a framework for measuring fair value and requires additional disclosures about the use of fair value measurements. Various inputs are considered when determining the value of the Company's investments, pension plan assets, long-term debt and interest rate derivatives. The inputs or methodologies used for valuing securities are not necessarily an indication of the risk associated with investing in these securities. These inputs are summarized in the three broad levels listed below. •Level 1 - observable market inputs that are unadjusted quoted prices for identical assets or liabilities in active markets; •Level 2 - other significant observable inputs (including quoted prices for similar securities, interest rates, credit risk, etc.); and •Level 3 - significant unobservable inputs (including the Company's own assumptions about the assumptions market participants would use in determining the fair value of investments). The valuation methods described below may produce a fair value calculation that may not be indicative of net realizable value or reflective of future fair values. Furthermore, while the Company believes its valuation methods are appropriate and consistent with other market participants, the use of different methodologies or assumptions to determine the fair value of certain financial instruments could result in a different fair value measurement at the reporting date. Investments The Company's investment assets, valued with assistance from a third-party trustee, consist of certificates of deposits, commercial paper, corporate bonds and government securities and are carried at fair value on the consolidated balance sheet per the Fair Value Measurements and Disclosures Topic in the ASC. There are several valuation methodologies used for those assets as described below. •Commercial Paper and Certificates of Deposit (Level 2): Valued at amortized cost, which approximates fair value; and •Corporate Bonds and Government Securities (Level 2): Valued using broker quotes that utilize observable market inputs. Long-term Debt Long-term debt is reported at carrying amount on the consolidated balance sheets and is the Company's only financial instrument with fair values significantly different from their carrying amounts. The majority of the Company's long-term debt is valued with assistance from a third party that utilizes closing transactions, market quotes or market values of comparable debt. For those instruments not valued by the third party, the fair value has been estimated by applying market rates of similar instruments to the scheduled contractual debt payments and maturities. These market rates are provided by the same third party. All of the inputs used to determine the fair value of the Company's long-term debt are Level 2 inputs. The fair value of outstanding debt fluctuates with changes in a number of factors. Such factors include, but are not limited to, interest rates, market conditions, credit ratings, values of similar financial instruments, size of the transaction, cash flow projections and comparable trades. Fair value will exceed carrying value when the current market interest rate is lower than the interest rate at which the debt was originally issued. The fair value of a company's debt is a measure of its current value under present market conditions. It does not impact the financial statements under current accounting rules.Interest Rate DerivativesThe Company’s forward starting interest rate swap is carried at fair value and is valued with assistance from a third party based upon pricing models using inputs observed from actively quoted markets. All of the inputs used to determine the fair value of the swap are Level 2 inputs.

Nature of Operations and Significant Accounting Policies (Policies)

6 Months Ended

Jun. 30, 2020

Organization, Consolidation and Presentation of Financial Statements [Abstract]

In the opinion of management, the accompanying consolidated financial statements contain all normal, recurring adjustments necessary to fairly present the consolidated financial statements and accompanying notes. Where applicable, prior year information has been reclassified to conform to the current presentation. Pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”), certain information and disclosures normally included in the notes to the annual financial statements prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) have been omitted from these interim financial statements. CSX suggests that these financial statements be read in conjunction with the audited financial statements and the notes included in CSX's most recent annual report on Form 10-K and any subsequently filed current reports on Form 8-K.

Fiscal Year

The Company's fiscal periods are based upon the calendar year. Except as otherwise specified, references to “second quarter(s)” or “six months” indicate CSX's fiscal periods ending June 30, 2020 and June 30, 2019, and references to "year-end" indicate the fiscal year ended December 31, 2019.

New Accounting Pronouncements

In June 2016, the FASB issued ASU Measurement of Credit Losses on Financial Instruments, which replaces current methods for evaluating impairment of financial instruments not measured at fair value, including trade accounts receivable and certain debt securities, with a current expected credit loss model. CSX adopted this new standard update effective January 1, 2020, and it did not have a material effect on the Company's results of operations.

In August 2018, the FASB issued ASU Changes to the Disclosure Requirements for Defined Benefit Plans as part of its disclosure effectiveness initiative, which modifies the disclosure requirements for employer-sponsored defined benefit pension and other postretirement plans. This update is effective for the Company beginning January 1, 2021 and adoption of the standard is not expected to significantly impact the Company's disclosures.

Revenue Recognition

The Company generates revenue from freight billings under contracts with customers generally on a rate per carload, container or ton-basis based on length of haul and commodities carried. The Company’s performance obligation arises when it receives a bill of lading (“BOL”) to transport a customer's commodities at a negotiated price contained in a transportation services agreement or a publicly disclosed tariff rate. Once a BOL is received, a contract is formed whereby the parties are committed to perform, collectability of consideration is probable and the rights of the parties, shipping terms and conditions, and payment terms are identified. A customer may submit several BOLs for transportation services at various times throughout a service agreement term but each shipment represents a distinct service that is a separately identified performance obligation.

NOTE 8. Revenues, continued

The average transit time to complete a shipment is between 3 to 8 days depending on market. Payments for transportation services are normally billed once a BOL is received and are generally due within 15 days after the invoice date. The Company recognizes revenue over transit time of freight as it moves from origin to destination. Revenue for services started but not completed at the reporting date is allocated based on the relative transit time in each reporting period, with the portion allocated for services subsequent to the reporting date considered remaining performance obligations.

The certain key estimates included in the recognition and measurement of revenue and related accounts receivable are as follows:

•Revenue associated with shipments in transit is recognized ratably over transit time and is based on average cycle times to move commodities and products from their origin to their final destination or interchange;

•Adjustments to revenue for billing corrections and billing discounts;

•Adjustments to revenue for overcharge claims filed by customers, which are based on historical payments to customers for rate overcharges as a percentage of total billing; and

•Incentive-based refunds to customers, which are primarily volume-related, are recorded as a reduction to revenue on the basis of the projected liability (this estimate is based on historical activity, current volume levels and forecasted future volume).

Revenue related to interline transportation services that involve the services of another party, such as another railroad, is reported on a net basis. The portion of the gross amount billed to customers that is remitted by the Company to another party is not reflected as revenue.

Other revenue is comprised of revenue from regional subsidiary railroads and incidental charges, including demurrage and switching. It is recorded upon completion of the service and accounts for an immaterial percentage of the Company's total revenue. Revenue from regional subsidiary railroads includes shipments by railroads that the Company does not directly operate. Demurrage represents charges assessed when freight cars are held by a customer beyond a specified period of time. Switching represents charges assessed when a railroad switches cars for a customer or another railroad.

During the second quarters and six months ended 2020 and 2019, revenue recognized from performance obligations related to prior periods (for example, due to changes in transaction price), was not material.

Remaining performance obligations represent the transaction price allocated to future reporting periods for freight services started but not completed at the reporting date. This includes the unearned portion of billed and unbilled amounts for cancellable freight shipments in transit. The Company expects to recognize the unearned portion of revenue for freight services in transit within one week of the reporting date.The timing of revenue recognition, billings and cash collections results in accounts receivable and customer advances and deposits (contract liabilities) on the consolidated balance sheets. Freight receivables include amounts earned, billed and unbilled, and currently due from customers for transportation-related services. Non-freight receivables include amounts billed and unbilled and currently due related to government reimbursement receivables and other non-revenue receivables. The Company maintains an allowance for credit losses to provide for the estimated amount of receivables that will not be collected. The allowance is based upon an assessment of risk characteristics, historical payment experience, and the age of outstanding receivables adjusted for forward-looking economic conditions as necessary.

Fair Value Measurements

The Financial Instruments Topic in the ASC requires disclosures about fair value of financial instruments in annual reports as well as in quarterly reports. For CSX, this statement applies to certain investments, long-term debt and interest rate derivatives. Disclosure of the fair value of pension plan assets is only required annually. Also, this rule clarifies the definition of fair value for financial reporting, establishes a framework for measuring fair value and requires additional disclosures about the use of fair value measurements.

Various inputs are considered when determining the value of the Company's investments, pension plan assets, long-term debt and interest rate derivatives. The inputs or methodologies used for valuing securities are not necessarily an indication of the risk associated with investing in these securities. These inputs are summarized in the three broad levels listed below.

•Level 1 - observable market inputs that are unadjusted quoted prices for identical assets or liabilities in active markets;

•Level 2 - other significant observable inputs (including quoted prices for similar securities, interest rates, credit risk, etc.); and

•Level 3 - significant unobservable inputs (including the Company's own assumptions about the assumptions market participants would use in determining the fair value of investments).

The valuation methods described below may produce a fair value calculation that may not be indicative of net realizable value or reflective of future fair values. Furthermore, while the Company believes its valuation methods are appropriate and consistent with other market participants, the use of different methodologies or assumptions to determine the fair value of certain financial instruments could result in a different fair value measurement at the reporting date.

Investments

The Company's investment assets, valued with assistance from a third-party trustee, consist of certificates of deposits, commercial paper, corporate bonds and government securities and are carried at fair value on the consolidated balance sheet per the Fair Value Measurements and Disclosures Topic in the ASC. There are several valuation methodologies used for those assets as described below.

•Commercial Paper and Certificates of Deposit (Level 2): Valued at amortized cost, which approximates fair value; and

•Corporate Bonds and Government Securities (Level 2): Valued using broker quotes that utilize observable market inputs.

Long-term Debt

Long-term debt is reported at carrying amount on the consolidated balance sheets and is the Company's only financial instrument with fair values significantly different from their carrying amounts. The majority of the Company's long-term debt is valued with assistance from a third party that utilizes closing transactions, market quotes or market values of comparable debt. For those instruments not valued by the third party, the fair value has been estimated by applying market rates of similar instruments to the scheduled contractual debt payments and maturities. These market rates are provided by the same third party. All of the inputs used to determine the fair value of the Company's long-term debt are Level 2 inputs.

The fair value of outstanding debt fluctuates with changes in a number of factors. Such factors include, but are not limited to, interest rates, market conditions, credit ratings, values of similar financial instruments, size of the transaction, cash flow projections and comparable trades. Fair value will exceed carrying value when the current market interest rate is lower than the interest rate at which the debt was originally issued. The fair value of a company's debt is a measure of its current value under present market conditions. It does not impact the financial statements under current accounting rules.Interest Rate DerivativesThe Company’s forward starting interest rate swap is carried at fair value and is valued with assistance from a third party based upon pricing models using inputs observed from actively quoted markets. All of the inputs used to determine the fair value of the swap are Level 2 inputs.