Summarized Consolidating Financial Data (Cash Flow Statements) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 30, 2016	Dec. 25, 2015	Dec. 26, 2014
Operating Activities
Net Cash Provided by (Used in) Operating Activities	$ 3,041	$ 3,370	$ 3,343
Investing Activities
Property Additions	(2,398)	(2,562)	(2,449)
Purchase of Short-term Investments	(929)	(1,739)	(1,433)
Proceeds from Sales of Short-term Investments	1,325	1,225	1,674
Proceeds from Property Dispositions	195	147	62
Other Investing Activities	9	37	(37)
Net Cash Used in Investing Activities	(1,798)	(2,892)	(2,183)
Financing Activities
Long-term Debt Issued	2,200	1,200	1,000
Long-term Debt Repaid	(1,419)	(229)	(933)
Dividends Paid	(680)	(686)	(629)
Shares Repurchased	(1,056)	(804)	(517)
Other Financing Activities	(313)	0	(4)
Net Cash Used in Financing Activities	(1,268)	(519)	(1,083)
Net (Decrease) Increase in Cash and Cash Equivalents	(25)	(41)	77
Cash and Cash Equivalents at Beginning of Period	628	669	592
Cash and Cash Equivalents at End of Period	603	628	669
CSX Corporation
Operating Activities
Net Cash Provided by (Used in) Operating Activities	453	983	583
Investing Activities
Property Additions	0	0	0
Purchase of Short-term Investments	(929)	(1,734)	(1,419)
Proceeds from Sales of Short-term Investments	1,325	1,175	1,642
Proceeds from Property Dispositions	0	0	0
Other Investing Activities	(41)	(10)	0
Net Cash Used in Investing Activities	355	(569)	223
Financing Activities
Long-term Debt Issued	2,200	1,200	1,000
Long-term Debt Repaid	(1,400)	(200)	(600)
Dividends Paid	(680)	(686)	(629)
Shares Repurchased	(1,056)	(804)	(517)
Other Financing Activities	(11)	10	11
Net Cash Used in Financing Activities	(947)	(480)	(735)
Net (Decrease) Increase in Cash and Cash Equivalents	(139)	(66)	71
Cash and Cash Equivalents at Beginning of Period	444	510	439
Cash and Cash Equivalents at End of Period	305	444	510
CSX Transportation
Operating Activities
Net Cash Provided by (Used in) Operating Activities	2,950	2,974	3,278
Investing Activities
Property Additions	(2,208)	(2,400)	(2,192)
Purchase of Short-term Investments	0	0	0
Proceeds from Sales of Short-term Investments	0	0	0
Proceeds from Property Dispositions	195	147	62
Other Investing Activities	91	132	(128)
Net Cash Used in Investing Activities	(1,922)	(2,121)	(2,258)
Financing Activities
Long-term Debt Issued	0	0	0
Long-term Debt Repaid	(19)	(29)	(333)
Dividends Paid	(600)	(750)	(660)
Shares Repurchased	0	0	0
Other Financing Activities	(303)	1	(18)
Net Cash Used in Financing Activities	(922)	(778)	(1,011)
Net (Decrease) Increase in Cash and Cash Equivalents	106	75	9
Cash and Cash Equivalents at Beginning of Period	175	100	91
Cash and Cash Equivalents at End of Period	281	175	100
Eliminations and Other
Operating Activities
Net Cash Provided by (Used in) Operating Activities	(362)	(587)	(518)
Investing Activities
Property Additions	(190)	(162)	(257)
Purchase of Short-term Investments	0	(5)	(14)
Proceeds from Sales of Short-term Investments	0	50	32
Proceeds from Property Dispositions	0	0	0
Other Investing Activities	(41)	(85)	91
Net Cash Used in Investing Activities	(231)	(202)	(148)
Financing Activities
Long-term Debt Issued	0	0	0
Long-term Debt Repaid	0	0	0
Dividends Paid	600	750	660
Shares Repurchased	0	0	0
Other Financing Activities	1	(11)	3
Net Cash Used in Financing Activities	601	739	663
Net (Decrease) Increase in Cash and Cash Equivalents	8	(50)	(3)
Cash and Cash Equivalents at Beginning of Period	9	59	62
Cash and Cash Equivalents at End of Period	$ 17	$ 9	$ 59