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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, 2017
Sep. 23, 2016
Sep. 30, 2017
Sep. 23, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]        
Weighted-average grant date fair value (in dollars per share) $ 12.54   $ 12.83 $ 4.68
Stock options valuation assumptions:        
Annual dividend yield (as a percent)     1.50% 3.00%
Risk-free interest rate (as a percent)     2.20% 1.40%
Annualized volatility (as a percent)     27.10% 27.30%
Expected life (in years)   0 years 6 years 3 months 6 years 6 months
Other pricing model inputs:        
Weighted-average grant-date market price of CSX stock (in dollars per share)     $ 49.60 $ 24.13