Stock Plans and Share-Based Compensation - Narrative (Details)	Feb. 10, 2021 shares	May 31, 2018 USD ($) shares
LTIP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted (in shares)	610,000
LTIP \| Performance Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of grants with performance vesting, average annual operating income growth	0.50
Percentage of grants with performance vesting, cumulative free cash flow	50.00%
Number of equivalent shares of CSX common stock per unit of award (in shares)	1
LTIP \| Performance Units \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Payout percentage range for participants	0.00%
LTIP \| Performance Units \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Payout percentage range for participants	200.00%
LTIP \| Performance Units \| Certain Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted (in shares)	189,000
LTIP \| Performance Units \| Certain Executive Officers
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of payout subject to upward or downward adjustment (up to)	0.25
LTIP \| Performance Units \| Certain Executive Officers \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Payout percentage range for participants	250.00%
LTIP \| Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Term of stock options (in years)	10 years
Award vesting period (in years)	3 years
LTIP \| Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted (in shares)	163,000
Number of equivalent shares of CSX common stock per unit of award (in shares)	1
Award vesting period (in years)	3 years
ESPP \| Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock registered for ESPP (in shares)		4,000,000
Minimum payroll deduction percentage		1.00%
Maximum payroll deduction percentage		10.00%
Maximum stock value available for purchase \| $		$ 25,000
Percentage of shares market price		85.00%
Share offering period		6 months

Percentage Of Grants With Performance Vesting, Average Annual Operating Income Growth

No definition available.

Name:	csx_PercentageOfGrantsWithPerformanceVestingAverageAnnualOperatingIncomeGrowth
Namespace Prefix:	csx_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage Of Grants With Performance Vesting, Cumulative Free Cash Flow

+ References

No definition available.

+ Details

Name:	csx_PercentageOfGrantsWithPerformanceVestingCumulativeFreeCashFlow
Namespace Prefix:	csx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Share Based Compensation Arrangement by Share Based Payment Award, Equity Instruments Other than Options, Payout Percentage Adjustment

+ References

No definition available.

+ Details

Name:	csx_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsPayoutPercentageAdjustment
Namespace Prefix:	csx_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Equivalent Shares of Common Stock Per Unit

+ References

No definition available.

+ Details

Name:	csx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfEquivalentSharesOfCommonStockPerUnit
Namespace Prefix:	csx_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Share Based Compensation Arrangement by Share Based Payment Award Maximum Stock Value Purchased per Employee

+ References

No definition available.

+ Details

Name:	csx_ShareBasedCompensationArrangementbyShareBasedPaymentAwardMaximumStockValuePurchasedperEmployee
Namespace Prefix:	csx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other Than Options, Payout Percentage of Target

+ References

No definition available.

+ Details

Name:	csx_SharebasedCompensationArrangementbySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsPayoutPercentageofTarget
Namespace Prefix:	csx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Share-based Compensation Arrangement by Share-based Payment Award, Minimum Employee Subscription Rate

+ References

No definition available.

+ Details

Name:	csx_SharebasedCompensationArrangementbySharebasedPaymentAwardMinimumEmployeeSubscriptionRate
Namespace Prefix:	csx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Share-based Compensation Arrangement by Share-based Payment Award, Share Offering Period

+ References

No definition available.

+ Details

Name:	csx_SharebasedCompensationArrangementbySharebasedPaymentAwardShareOfferingPeriod
Namespace Prefix:	csx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Aggregate number of common shares reserved for future issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.29)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_CommonStockCapitalSharesReservedForFutureIssuance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The highest percentage of annual salary that an employee is permitted to utilize with respect to the plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeSubscriptionRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Gross number of share options (or share units) granted during the period.

+ References

No definition available.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Purchase price of common stock expressed as a percentage of its fair value.

+ References

No definition available.

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_PlanNameAxis=csx_LongtermIncentivePlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_PerformanceSharesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_TitleOfIndividualAxis=csx_CertainEmployeesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_TitleOfIndividualAxis=srt_ExecutiveOfficerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_EmployeeStockOptionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_RestrictedStockUnitsRSUMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=csx_EmployeeStockPurchasePlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_EmployeeStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: