Summarized Consolidating Financial Data (Consolidating Cash Flow Statements) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 30, 2016	Dec. 25, 2015
Operating Activities
Net Cash Provided by (Used in) Operating Activities	$ 3,472	$ 3,041	$ 3,370
Investing Activities
Property Additions	(2,040)	(2,398)	(2,562)
Purchase of Short-term Investments	(782)	(929)	(1,739)
Proceeds from Sales of Short-term Investments	1,193	1,325	1,225
Proceeds from Property Dispositions	97	195	147
Other Investing Activities	37	9	37
Net Cash Used in Investing Activities	(1,495)	(1,798)	(2,892)
Financing Activities
Long-term Debt Issued	850	2,200	1,200
Long-term Debt Repaid	(333)	(1,419)	(229)
Dividends Paid	(708)	(680)	(686)
Shares Repurchased	(1,970)	(1,056)	(804)
Other Financing Activities	(18)	(313)	0
Net Cash Used in Financing Activities	(2,179)	(1,268)	(519)
Net Decrease in Cash and Cash Equivalents	(202)	(25)	(41)
Cash and Cash Equivalents at Beginning of Period	603	628	669
Cash and Cash Equivalents at End of Period	401	603	628
Eliminations and Other
Operating Activities
Net Cash Provided by (Used in) Operating Activities	(359)	(362)	(587)
Investing Activities
Property Additions	(192)	(190)	(162)
Purchase of Short-term Investments	(8)	0	(5)
Proceeds from Sales of Short-term Investments	3	0	50
Proceeds from Property Dispositions	0	0	0
Other Investing Activities	(55)	(41)	(85)
Net Cash Used in Investing Activities	(252)	(231)	(202)
Financing Activities
Long-term Debt Issued	0	0	0
Long-term Debt Repaid	0	0	0
Dividends Paid	600	600	750
Shares Repurchased	0	0	0
Other Financing Activities	0	1	(11)
Net Cash Used in Financing Activities	600	601	739
Net Decrease in Cash and Cash Equivalents	(11)	8	(50)
Cash and Cash Equivalents at Beginning of Period	17	9	59
Cash and Cash Equivalents at End of Period	6	17	9
CSX Corporation
Operating Activities
Net Cash Provided by (Used in) Operating Activities	1,719	453	983
Investing Activities
Property Additions	0	0	0
Purchase of Short-term Investments	(774)	(929)	(1,734)
Proceeds from Sales of Short-term Investments	1,190	1,325	1,175
Proceeds from Property Dispositions	0	0	0
Other Investing Activities	(2)	(41)	(10)
Net Cash Used in Investing Activities	414	355	(569)
Financing Activities
Long-term Debt Issued	850	2,200	1,200
Long-term Debt Repaid	(313)	(1,400)	(200)
Dividends Paid	(708)	(680)	(686)
Shares Repurchased	(1,970)	(1,056)	(804)
Other Financing Activities	(23)	(11)	10
Net Cash Used in Financing Activities	(2,164)	(947)	(480)
Net Decrease in Cash and Cash Equivalents	(31)	(139)	(66)
Cash and Cash Equivalents at Beginning of Period	305	444	510
Cash and Cash Equivalents at End of Period	274	305	444
CSX Transportation
Operating Activities
Net Cash Provided by (Used in) Operating Activities	2,112	2,950	2,974
Investing Activities
Property Additions	(1,848)	(2,208)	(2,400)
Purchase of Short-term Investments	0	0	0
Proceeds from Sales of Short-term Investments	0	0	0
Proceeds from Property Dispositions	97	195	147
Other Investing Activities	94	91	132
Net Cash Used in Investing Activities	(1,657)	(1,922)	(2,121)
Financing Activities
Long-term Debt Issued	0	0	0
Long-term Debt Repaid	(20)	(19)	(29)
Dividends Paid	(600)	(600)	(750)
Shares Repurchased	0	0	0
Other Financing Activities	5	(303)	1
Net Cash Used in Financing Activities	(615)	(922)	(778)
Net Decrease in Cash and Cash Equivalents	(160)	106	75
Cash and Cash Equivalents at Beginning of Period	281	175	100
Cash and Cash Equivalents at End of Period	$ 121	$ 281	$ 175