Summarized Consolidating Financial Data - Consolidating Cash Flow Statements (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Operating Activities
Net Cash Provided by (Used in) Operating Activities			$ 2,009	$ 1,566
Investing Activities
Property Additions			(823)	(955)
Proceeds from Property Dispositions			141	16
Purchase of Short-term Investments			(77)	(545)
Proceeds from Sales of Short-term Investments			12	492
Other Investing Activities			(8)	25
Net Cash Used In Investing Activities			(755)	(967)
Financing Activities
Long-term Debt Issued			2,000	850
Long-term Debt Repaid			0	(313)
Dividends Paid			(384)	(350)
Shares Repurchased	$ (974)	$ (499)	(1,810)	(757)
Accelerated Share Repurchase Pending Final Settlement (Note 2)			(90)	0
Other Financing Activities			(51)	(12)
Net Cash Used in Financing Activities			(335)	(582)
Net Increase in Cash and Cash Equivalents			919	17
Cash and Cash Equivalents at Beginning of Period			401	603
Cash and Cash Equivalents at End of Period	1,320	620	1,320	620
Eliminations and Other
Operating Activities
Net Cash Provided by (Used in) Operating Activities			(547)	(221)
Investing Activities
Property Additions			(61)	(82)
Proceeds from Property Dispositions			0	0
Purchase of Short-term Investments			(2)	(6)
Proceeds from Sales of Short-term Investments			12	2
Other Investing Activities			92	(8)
Net Cash Used In Investing Activities			41	(94)
Financing Activities
Long-term Debt Issued			0	0
Long-term Debt Repaid			0	0
Dividends Paid			500	300
Shares Repurchased			0	0
Accelerated Share Repurchase Pending Final Settlement (Note 2)			0
Other Financing Activities			5	7
Net Cash Used in Financing Activities			505	307
Net Increase in Cash and Cash Equivalents			(1)	(8)
Cash and Cash Equivalents at Beginning of Period			6	17
Cash and Cash Equivalents at End of Period	5	9	5	9
CSX Corporation
Operating Activities
Net Cash Provided by (Used in) Operating Activities			1,311	814
Investing Activities
Property Additions			0	0
Proceeds from Property Dispositions			0	0
Purchase of Short-term Investments			(75)	(539)
Proceeds from Sales of Short-term Investments			0	490
Other Investing Activities			(1)	(2)
Net Cash Used In Investing Activities			(76)	(51)
Financing Activities
Long-term Debt Issued			2,000	850
Long-term Debt Repaid			0	(313)
Dividends Paid			(384)	(350)
Shares Repurchased			(1,810)	(757)
Accelerated Share Repurchase Pending Final Settlement (Note 2)			(90)
Other Financing Activities			(53)	(15)
Net Cash Used in Financing Activities			(337)	(585)
Net Increase in Cash and Cash Equivalents			898	178
Cash and Cash Equivalents at Beginning of Period			274	305
Cash and Cash Equivalents at End of Period	1,172	483	1,172	483
CSX Transportation
Operating Activities
Net Cash Provided by (Used in) Operating Activities			1,245	973
Investing Activities
Property Additions			(762)	(873)
Proceeds from Property Dispositions			141	16
Purchase of Short-term Investments			0	0
Proceeds from Sales of Short-term Investments			0	0
Other Investing Activities			(99)	35
Net Cash Used In Investing Activities			(720)	(822)
Financing Activities
Long-term Debt Issued			0	0
Long-term Debt Repaid			0	0
Dividends Paid			(500)	(300)
Shares Repurchased			0	0
Accelerated Share Repurchase Pending Final Settlement (Note 2)			0
Other Financing Activities			(3)	(4)
Net Cash Used in Financing Activities			(503)	(304)
Net Increase in Cash and Cash Equivalents			22	(153)
Cash and Cash Equivalents at Beginning of Period			121	281
Cash and Cash Equivalents at End of Period	$ 143	$ 128	$ 143	$ 128