Summarized Consolidating Financial Data - Consolidating Cash Flow Statements (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 24, 2016	Jun. 26, 2015	Jun. 24, 2016	Jun. 26, 2015
Operating Activities
Net Cash Provided by (Used in) Operating Activities			$ 1,592	$ 1,582
Investing Activities
Property Additions			(1,066)	(1,288)
Purchase of Short-term Investments			(260)	(775)
Proceeds from Sales of Short-term Investments			810	390
Proceeds from Property Dispositions			8	47
Other Investing Activities			27	52
Net Cash Used in Investing Activities			(481)	(1,574)
Financing Activities
Long-term Debt Issued			0	600
Long-term Debt Repaid			0	(210)
Dividends Paid			(344)	(336)
Stock Options Exercised			0	0
Shares Repurchased	$ (266)	$ (157)	(515)	(284)
Other Financing Activities			(314)	(9)
Net Cash Used in Financing Activities			(1,173)	(239)
Net Increase (Decrease) in Cash and Cash Equivalents			(62)	(231)
Cash and Cash Equivalents at Beginning of Period			628	669
Cash and Cash Equivalents at End of Period	566	438	566	438
CSX Corporation
Operating Activities
Net Cash Provided by (Used in) Operating Activities			295	367
Investing Activities
Property Additions			0	0
Purchase of Short-term Investments			(260)	(775)
Proceeds from Sales of Short-term Investments			810	355
Proceeds from Property Dispositions			0	0
Other Investing Activities			(2)	(11)
Net Cash Used in Investing Activities			548	(431)
Financing Activities
Long-term Debt Issued			0	600
Long-term Debt Repaid			0	(200)
Dividends Paid			(344)	(336)
Stock Options Exercised			0
Shares Repurchased			(515)	(284)
Other Financing Activities			(8)	7
Net Cash Used in Financing Activities			(867)	(213)
Net Increase (Decrease) in Cash and Cash Equivalents			(24)	(277)
Cash and Cash Equivalents at Beginning of Period			444	510
Cash and Cash Equivalents at End of Period	420	233	420	233
CSX Transportation
Operating Activities
Net Cash Provided by (Used in) Operating Activities			1,449	1,530
Investing Activities
Property Additions			(994)	(1,215)
Purchase of Short-term Investments			0	0
Proceeds from Sales of Short-term Investments			0	0
Proceeds from Property Dispositions			8	46
Other Investing Activities			96	72
Net Cash Used in Investing Activities			(890)	(1,097)
Financing Activities
Long-term Debt Issued			0	0
Long-term Debt Repaid			0	(10)
Dividends Paid			(300)	(375)
Stock Options Exercised			0
Shares Repurchased			0	0
Other Financing Activities			(307)	(4)
Net Cash Used in Financing Activities			(607)	(389)
Net Increase (Decrease) in Cash and Cash Equivalents			(48)	44
Cash and Cash Equivalents at Beginning of Period			175	100
Cash and Cash Equivalents at End of Period	127	144	127	144
Eliminations and Other
Operating Activities
Net Cash Provided by (Used in) Operating Activities			(152)	(315)
Investing Activities
Property Additions			(72)	(73)
Purchase of Short-term Investments			0	0
Proceeds from Sales of Short-term Investments			0	35
Proceeds from Property Dispositions			0	1
Other Investing Activities			(67)	(9)
Net Cash Used in Investing Activities			(139)	(46)
Financing Activities
Long-term Debt Issued			0	0
Long-term Debt Repaid			0	0
Dividends Paid			300	375
Stock Options Exercised			0	0
Shares Repurchased			0	0
Other Financing Activities			1	(12)
Net Cash Used in Financing Activities			301	363
Net Increase (Decrease) in Cash and Cash Equivalents			10	2
Cash and Cash Equivalents at Beginning of Period			9	59
Cash and Cash Equivalents at End of Period	$ 19	$ 61	$ 19	$ 61