Summarized Consolidating Financial Data (Consolidating Cash Flow Statements) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 30, 2016
Operating Activities
Net Cash Provided by (Used in) Operating Activities	$ 4,641	$ 3,472	$ 3,041
Investing Activities
Property Additions	(1,745)	(2,040)	(2,398)
Purchase of Short-term Investments	(736)	(782)	(929)
Proceeds from Sales of Short-term Investments	505	1,193	1,325
Proceeds from Property Dispositions	319	97	195
Other Investing Activities	(27)	37	9
Net Cash Used in Investing Activities	(1,684)	(1,495)	(1,798)
Financing Activities
Long-term Debt Issued	3,000	850	2,200
Long-term Debt Repaid	(19)	(333)	(1,419)
Dividends Paid	(751)	(708)	(680)
Shares Repurchased	(4,671)	(1,970)	(1,056)
Other Financing Activities	(59)	(18)	(313)
Net Cash Used in Financing Activities	(2,500)	(2,179)	(1,268)
Net Increase (Decrease) in Cash and Cash Equivalents	457	(202)	(25)
Cash and Cash Equivalents at Beginning of Period	401	603	628
Cash and Cash Equivalents at End of Period	858	401	603
Eliminations and Other
Operating Activities
Net Cash Provided by (Used in) Operating Activities	(198)	(359)	(362)
Investing Activities
Property Additions	(165)	(192)	(190)
Purchase of Short-term Investments	(2)	(8)	0
Proceeds from Sales of Short-term Investments	20	3	0
Proceeds from Property Dispositions	0	0	0
Other Investing Activities	(661)	(55)	(41)
Net Cash Used in Investing Activities	(808)	(252)	(231)
Financing Activities
Long-term Debt Issued	0	0	0
Long-term Debt Repaid	0	0	0
Dividends Paid	1,000	600	600
Shares Repurchased	0	0	0
Other Financing Activities	12	0	1
Net Cash Used in Financing Activities	1,012	600	601
Net Increase (Decrease) in Cash and Cash Equivalents	6	(11)	8
Cash and Cash Equivalents at Beginning of Period	6	17	9
Cash and Cash Equivalents at End of Period	12	6	17
CSX Corporation
Operating Activities
Net Cash Provided by (Used in) Operating Activities	3,182	1,719	453
Investing Activities
Property Additions	0	0	0
Purchase of Short-term Investments	(734)	(774)	(929)
Proceeds from Sales of Short-term Investments	485	1,190	1,325
Proceeds from Property Dispositions	0	0	0
Other Investing Activities	(4)	(2)	(41)
Net Cash Used in Investing Activities	(253)	414	355
Financing Activities
Long-term Debt Issued	3,000	850	2,200
Long-term Debt Repaid	0	(313)	(1,400)
Dividends Paid	(751)	(708)	(680)
Shares Repurchased	(4,671)	(1,970)	(1,056)
Other Financing Activities	(65)	(23)	(11)
Net Cash Used in Financing Activities	(2,487)	(2,164)	(947)
Net Increase (Decrease) in Cash and Cash Equivalents	442	(31)	(139)
Cash and Cash Equivalents at Beginning of Period	274	305	444
Cash and Cash Equivalents at End of Period	716	274	305
CSX Transportation
Operating Activities
Net Cash Provided by (Used in) Operating Activities	1,657	2,112	2,950
Investing Activities
Property Additions	(1,580)	(1,848)	(2,208)
Purchase of Short-term Investments	0	0	0
Proceeds from Sales of Short-term Investments	0	0	0
Proceeds from Property Dispositions	319	97	195
Other Investing Activities	638	94	91
Net Cash Used in Investing Activities	(623)	(1,657)	(1,922)
Financing Activities
Long-term Debt Issued	0	0	0
Long-term Debt Repaid	(19)	(20)	(19)
Dividends Paid	(1,000)	(600)	(600)
Shares Repurchased	0	0	0
Other Financing Activities	(6)	5	(303)
Net Cash Used in Financing Activities	(1,025)	(615)	(922)
Net Increase (Decrease) in Cash and Cash Equivalents	9	(160)	106
Cash and Cash Equivalents at Beginning of Period	121	281	175
Cash and Cash Equivalents at End of Period	$ 130	$ 121	$ 281