Summarized Consolidating Financial Data (Cash Flow Statements) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 25, 2015	Dec. 26, 2014	Dec. 27, 2013
Operating Activities
Net Cash Provided by (Used in) Operating Activities	$ 3,370	$ 3,343	$ 3,267
Investing Activities
Property Additions	(2,562)	(2,449)	(2,313)
Purchase of Short-term Investments	(1,739)	(1,433)	(1,256)
Proceeds from Sales of Short-term Investments	1,225	1,674	1,401
Proceeds from Property Dispositions	147	62	53
Other Investing Activities	37	(37)	(112)
Net Cash Used in Investing Activities	(2,892)	(2,183)	(2,227)
Financing Activities
Long-term Debt Issued	1,200	1,000	500
Long-term Debt Repaid	(229)	(933)	(780)
Dividends Paid	(686)	(629)	(600)
Stock Options Exercised	0	0	9
Shares Repurchased	(804)	(517)	(353)
Other Financing Activities	0	(4)	(8)
Net Cash Used in Financing Activities	(519)	(1,083)	(1,232)
Net (Decrease) Increase in Cash and Cash Equivalents	(41)	77	(192)
Cash and Cash Equivalents at Beginning of Period	669	592	784
Cash and Cash Equivalents at End of Period	628	669	592
CSX Corporation
Operating Activities
Net Cash Provided by (Used in) Operating Activities	983	583	1,004
Investing Activities
Property Additions	0	0	0
Purchase of Short-term Investments	(1,734)	(1,419)	(1,251)
Proceeds from Sales of Short-term Investments	1,175	1,642	1,335
Proceeds from Property Dispositions	0	0	0
Other Investing Activities	(10)	0	(134)
Net Cash Used in Investing Activities	(569)	223	(50)
Financing Activities
Long-term Debt Issued	1,200	1,000	500
Long-term Debt Repaid	(200)	(600)	(700)
Dividends Paid	(686)	(629)	(600)
Stock Options Exercised	0	0	9
Shares Repurchased	(804)	(517)	(353)
Other Financing Activities	10	11	148
Net Cash Used in Financing Activities	(480)	(735)	(996)
Net (Decrease) Increase in Cash and Cash Equivalents	(66)	71	(42)
Cash and Cash Equivalents at Beginning of Period	510	439	481
Cash and Cash Equivalents at End of Period	444	510	439
CSX Transportation
Operating Activities
Net Cash Provided by (Used in) Operating Activities	2,974	3,278	3,005
Investing Activities
Property Additions	(2,400)	(2,192)	(2,053)
Purchase of Short-term Investments	0	0	0
Proceeds from Sales of Short-term Investments	0	0	0
Proceeds from Property Dispositions	147	62	53
Other Investing Activities	132	(128)	(315)
Net Cash Used in Investing Activities	(2,121)	(2,258)	(2,315)
Financing Activities
Long-term Debt Issued	0	0	0
Long-term Debt Repaid	(29)	(333)	(80)
Dividends Paid	(750)	(660)	(730)
Stock Options Exercised	0	0	0
Shares Repurchased	0	0	0
Other Financing Activities	1	(18)	(24)
Net Cash Used in Financing Activities	(778)	(1,011)	(834)
Net (Decrease) Increase in Cash and Cash Equivalents	75	9	(144)
Cash and Cash Equivalents at Beginning of Period	100	91	235
Cash and Cash Equivalents at End of Period	175	100	91
Eliminations and Other
Operating Activities
Net Cash Provided by (Used in) Operating Activities	(587)	(518)	(742)
Investing Activities
Property Additions	(162)	(257)	(260)
Purchase of Short-term Investments	(5)	(14)	(5)
Proceeds from Sales of Short-term Investments	50	32	66
Proceeds from Property Dispositions	0	0	0
Other Investing Activities	(85)	91	337
Net Cash Used in Investing Activities	(202)	(148)	138
Financing Activities
Long-term Debt Issued	0	0	0
Long-term Debt Repaid	0	0	0
Dividends Paid	750	660	730
Stock Options Exercised	0	0	0
Shares Repurchased	0	0	0
Other Financing Activities	(11)	3	(132)
Net Cash Used in Financing Activities	739	663	598
Net (Decrease) Increase in Cash and Cash Equivalents	(50)	(3)	(6)
Cash and Cash Equivalents at Beginning of Period	59	62	68
Cash and Cash Equivalents at End of Period	$ 9	$ 59	$ 62