Summarized Consolidating Financial Data - Consolidating Cash Flow Statements (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Operating Activities
Net Cash Provided by (Used in) Operating Activities			$ 3,406	$ 2,861
Investing Activities
Property Additions			(1,240)	(1,462)
Proceeds from Property Dispositions			257	38
Purchase of Short-term Investments			(611)	(645)
Proceeds from Sales of Short-term Investments			15	957
Other Investing Activities			(8)	33
Net Cash Used In Investing Activities			(1,587)	(1,079)
Financing Activities
Long-term Debt Issued			2,000	850
Long-term Debt Repaid			(19)	(332)
Dividends Paid			(570)	(530)
Shares Repurchased	$ (1,000)	$ (1,000)	(2,816)	(1,763)
Accelerated Share Repurchase Pending Final Settlement (Note 2)			(100)	0
Other Financing Activities			(52)	(19)
Net Cash Used in Financing Activities			(1,557)	(1,794)
Net Increase (Decrease) in Cash and Cash Equivalents			262	(12)
Cash and Cash Equivalents at Beginning of Period			401	603
Cash and Cash Equivalents at End of Period	663	591	663	591
Eliminations and Other
Operating Activities
Net Cash Provided by (Used in) Operating Activities			(803)	(273)
Investing Activities
Property Additions			(106)	(151)
Proceeds from Property Dispositions			0	0
Purchase of Short-term Investments			(2)	(6)
Proceeds from Sales of Short-term Investments			15	2
Other Investing Activities			142	(25)
Net Cash Used In Investing Activities			49	(180)
Financing Activities
Long-term Debt Issued			0	0
Long-term Debt Repaid			0	0
Dividends Paid			750	450
Shares Repurchased			0	0
Accelerated Share Repurchase Pending Final Settlement (Note 2)			0
Other Financing Activities			8	(3)
Net Cash Used in Financing Activities			758	447
Net Increase (Decrease) in Cash and Cash Equivalents			4	(6)
Cash and Cash Equivalents at Beginning of Period			6	17
Cash and Cash Equivalents at End of Period	10	11	10	11
CSX Corporation
Operating Activities
Net Cash Provided by (Used in) Operating Activities			2,417	1,590
Investing Activities
Property Additions			0	0
Proceeds from Property Dispositions			0	0
Purchase of Short-term Investments			(609)	(639)
Proceeds from Sales of Short-term Investments			0	955
Other Investing Activities			(1)	(2)
Net Cash Used In Investing Activities			(610)	314
Financing Activities
Long-term Debt Issued			2,000	850
Long-term Debt Repaid			0	(312)
Dividends Paid			(570)	(530)
Shares Repurchased			(2,816)	(1,763)
Accelerated Share Repurchase Pending Final Settlement (Note 2)			(100)
Other Financing Activities			(58)	(21)
Net Cash Used in Financing Activities			(1,544)	(1,776)
Net Increase (Decrease) in Cash and Cash Equivalents			263	128
Cash and Cash Equivalents at Beginning of Period			274	305
Cash and Cash Equivalents at End of Period	537	433	537	433
CSX Transportation
Operating Activities
Net Cash Provided by (Used in) Operating Activities			1,792	1,544
Investing Activities
Property Additions			(1,134)	(1,311)
Proceeds from Property Dispositions			257	38
Purchase of Short-term Investments			0	0
Proceeds from Sales of Short-term Investments			0	0
Other Investing Activities			(149)	60
Net Cash Used In Investing Activities			(1,026)	(1,213)
Financing Activities
Long-term Debt Issued			0	0
Long-term Debt Repaid			(19)	(20)
Dividends Paid			(750)	(450)
Shares Repurchased			0	0
Accelerated Share Repurchase Pending Final Settlement (Note 2)			0
Other Financing Activities			(2)	5
Net Cash Used in Financing Activities			(771)	(465)
Net Increase (Decrease) in Cash and Cash Equivalents			(5)	(134)
Cash and Cash Equivalents at Beginning of Period			121	281
Cash and Cash Equivalents at End of Period	$ 116	$ 147	$ 116	$ 147