Summarized Consolidating Financial Data - Consolidating Cash Flow Statements (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating Activities
Net Cash Provided by (Used in) Operating Activities	$ 966	$ 1,043
Investing Activities
Property Additions	(368)	(441)
Proceeds from Property Dispositions	52	13
Purchase of Short-term Investments	0	(75)
Proceeds from Sales of Short-term Investments	8	205
Other Investing Activities	(8)	12
Net Cash Used In Investing Activities	(316)	(286)
Financing Activities
Long-term Debt Issued	2,000	0
Long-term Debt Repaid	0
Dividends Paid	(194)	(166)
Shares Repurchased	(836)	(258)
Other Financing Activities	(41)	(6)
Net Cash Provided By (Used in) Financing Activities	929	(430)
Net Increase in Cash and Cash Equivalents	1,579	327
Cash and Cash Equivalents at Beginning of Period	401	603
Cash and Cash Equivalents at End of Period	1,980	930
Eliminations and Other
Operating Activities
Net Cash Provided by (Used in) Operating Activities	(346)	(167)
Investing Activities
Property Additions	(29)	(44)
Purchase of Short-term Investments	0	0
Proceeds from Sales of Short-term Investments	8	0
Other Investing Activities	113	42
Net Cash Used In Investing Activities	92	6
Financing Activities
Long-term Debt Issued	0
Long-term Debt Repaid	0
Dividends Paid	250	150
Shares Repurchased	0	0
Other Financing Activities	3	4
Net Cash Provided By (Used in) Financing Activities	253	154
Net Increase in Cash and Cash Equivalents	(1)	(7)
Cash and Cash Equivalents at Beginning of Period	6	17
Cash and Cash Equivalents at End of Period	5	10
CSX Corporation
Operating Activities
Net Cash Provided by (Used in) Operating Activities	691	644
Investing Activities
Property Additions	0	0
Proceeds from Property Dispositions	0	0
Purchase of Short-term Investments	0	(75)
Proceeds from Sales of Short-term Investments	0	205
Other Investing Activities	(1)	(1)
Net Cash Used In Investing Activities	(1)	129
Financing Activities
Long-term Debt Issued	2,000
Long-term Debt Repaid	0
Dividends Paid	(194)	(166)
Shares Repurchased	(836)	(258)
Other Financing Activities	(40)	(6)
Net Cash Provided By (Used in) Financing Activities	930	(430)
Net Increase in Cash and Cash Equivalents	1,620	343
Cash and Cash Equivalents at Beginning of Period	274	305
Cash and Cash Equivalents at End of Period	1,894	648
CSX Transportation
Operating Activities
Net Cash Provided by (Used in) Operating Activities	621	566
Investing Activities
Property Additions	(339)	(397)
Proceeds from Property Dispositions	52	5
Purchase of Short-term Investments	0	0
Proceeds from Sales of Short-term Investments	0	0
Other Investing Activities	(120)	(29)
Net Cash Used In Investing Activities	(407)	(421)
Financing Activities
Long-term Debt Issued	0
Long-term Debt Repaid	0
Dividends Paid	(250)	(150)
Shares Repurchased	0	0
Other Financing Activities	(4)	(4)
Net Cash Provided By (Used in) Financing Activities	(254)	(154)
Net Increase in Cash and Cash Equivalents	(40)	(9)
Cash and Cash Equivalents at Beginning of Period	121	281
Cash and Cash Equivalents at End of Period	81	272
Consolidation Eliminations and Other Entities [Member]
Investing Activities
Proceeds from Property Dispositions	$ 0	$ 8