Summarized Consolidating Financial Data (Income Statements) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 25, 2015	Sep. 25, 2015	Jun. 26, 2015	Mar. 27, 2015	Dec. 26, 2014	Sep. 26, 2014	Jun. 27, 2014	Mar. 28, 2014	Dec. 25, 2015	Dec. 26, 2014	Dec. 27, 2013
Consolidated Income Statement
Revenue	$ 2,781	$ 2,939	$ 3,064	$ 3,027	$ 3,192	$ 3,221	$ 3,244	$ 3,012	$ 11,811	$ 12,669	$ 12,026
Expense									8,227	9,056	8,553
Operating Income	791	933	1,017	843	901	976	997	739	3,584	3,613	3,473
Equity in Earnings of Subsidiaries									0	0	0
Interest Expense									(544)	(545)	(562)
Other Income - Net									98	(24)	11
Earnings Before Income Taxes									3,138	3,044	2,922
Income Tax Benefit (Expense)									(1,170)	(1,117)	(1,058)
Net Earnings	$ 466	$ 507	$ 553	$ 442	$ 491	$ 509	$ 529	$ 398	1,968	1,927	1,864
Total Comprehensive Earnings									1,969	1,784	2,277
CSX Corporation
Consolidated Income Statement
Revenue									0	0	0
Expense									(589)	(427)	(371)
Operating Income									589	427	371
Equity in Earnings of Subsidiaries									1,949	1,996	1,964
Interest Expense									(539)	(520)	(516)
Other Income - Net									(4)	(19)	(7)
Earnings Before Income Taxes									1,995	1,884	1,812
Income Tax Benefit (Expense)									(27)	43	52
Net Earnings									1,968	1,927	1,864
Total Comprehensive Earnings									1,969	1,784	2,277
CSX Transportation
Consolidated Income Statement
Revenue									11,733	12,590	11,950
Expense									8,922	9,585	9,091
Operating Income									2,811	3,005	2,859
Equity in Earnings of Subsidiaries									0	1	(1)
Interest Expense									(33)	(46)	(62)
Other Income - Net									111	(4)	(2)
Earnings Before Income Taxes									2,889	2,956	2,794
Income Tax Benefit (Expense)									(1,083)	(1,093)	(1,028)
Net Earnings									1,806	1,863	1,766
Total Comprehensive Earnings									1,806	1,875	1,825
Eliminations and Other
Consolidated Income Statement
Revenue									78	79	76
Expense									(106)	(102)	(167)
Operating Income									184	181	243
Equity in Earnings of Subsidiaries									(1,949)	(1,997)	(1,963)
Interest Expense									28	21	16
Other Income - Net									(9)	(1)	20
Earnings Before Income Taxes									(1,746)	(1,796)	(1,684)
Income Tax Benefit (Expense)									(60)	(67)	(82)
Net Earnings									(1,806)	(1,863)	(1,766)
Total Comprehensive Earnings									$ (1,806)	$ (1,875)	$ (1,825)