Share-Based Compensation - Summary of Fair Value Assumptions for Stock Option Awards (Details) - $ / shares	1 Months Ended	3 Months Ended	9 Months Ended
Feb. 28, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant date fair value (in dollars per share)	$ 14.55
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant date fair value (in dollars per share)		$ 20.52	$ 0.00	$ 14.65	$ 12.83
Stock options valuation assumptions:
Annual dividend yield (as a percent)		1.20%	0.00%	1.50%	1.50%
Risk-free interest rate (as a percent)		2.80%	0.00%	2.60%	2.20%
Annualized volatility (as a percent)		25.50%	0.00%	27.00%	27.10%
Expected life (in years)		6 years 6 months	0 years	6 years 6 months	6 years 3 months
Other pricing model inputs:
Weighted-average grant-date market price of CSX stock (in dollars per share)		$ 74.84	$ 0.00	$ 54.19	$ 49.60

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- Definition

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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The risk-free interest rate assumption that is used in valuing an option on its own shares.

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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.

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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- Definition

Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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