Summarized Consolidating Financial Data (Consolidating Balance Sheets) (Details) - USD ($) $ / shares in Units, $ in Millions	Dec. 31, 2017	Dec. 30, 2016	Dec. 25, 2015	Dec. 26, 2014
Current Assets:
Cash and Cash Equivalents	$ 401	$ 603	$ 628	$ 669
Short-term Investments	18	417
Accounts Receivable - Net	970	938
Receivable from Affiliates	0	0
Materials and Supplies	372	407
Other Current Assets	154	122
Total Current Assets	1,915	2,487
Properties	44,324	43,227
Accumulated Depreciation	(12,560)	(12,077)
Properties - Net	31,764	31,150
Other Long-term Assets	374	318
Total Assets	35,739	35,414
Current Liabilities:
Accounts Payable	847	806
Labor and Fringe Benefits Payable	602	545
Payable to Affiliates	0	0
Casualty, Environmental and Other Reserves	108	115
Current Maturities of Long-term Debt	19	331
Income and Other Taxes Payable	157	129
Other Current Liabilities	161	114
Total Current Liabilities	1,894	2,040
Casualty, Environmental and Other Reserves	266	259
Long-term Debt	11,790	10,962
Deferred Income Taxes - Net	6,418	9,596
Other Long-term Liabilities	650	863
Total Liabilities	21,018	23,720
Shareholders' Equity:
Common Stock, $1 Par Value	890	928
Other Capital	217	138
Retained Earnings	14,084	11,253
Accumulated Other Comprehensive Loss	(486)	(640)
Noncontrolling Minority Interest	16	15
Total Shareholders' Equity	14,721	11,694	11,668	11,176
Total Liabilities and Shareholders' Equity	$ 35,739	$ 35,414
Common stock par value (in dollars per share)	$ 1	$ 1
Investments in Conrail
Current Assets:
Investment in Affiliates, Subsidiaries and Other	$ 907	$ 840
Affiliates and Other Companies
Current Assets:
Investment in Affiliates, Subsidiaries and Other	779	619
Investment in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates, Subsidiaries and Other	0	0
Eliminations and Other
Current Assets:
Cash and Cash Equivalents	6	17	9	59
Short-term Investments	18	2
Accounts Receivable - Net	670	721
Receivable from Affiliates	(4,743)	(3,508)
Materials and Supplies	0	0
Other Current Assets	10	16
Total Current Assets	(4,039)	(2,752)
Properties	2,844	2,708
Accumulated Depreciation	(1,542)	(1,442)
Properties - Net	1,302	1,266
Other Long-term Assets	(261)	(291)
Total Assets	(31,478)	(25,101)
Current Liabilities:
Accounts Payable	34	33
Labor and Fringe Benefits Payable	56	65
Payable to Affiliates	(5,344)	(3,957)
Casualty, Environmental and Other Reserves	13	13
Current Maturities of Long-term Debt	0	(1)
Income and Other Taxes Payable	28	16
Other Current Liabilities	3	2
Total Current Liabilities	(5,210)	(3,829)
Casualty, Environmental and Other Reserves	44	51
Long-term Debt	1	0
Deferred Income Taxes - Net	206	258
Other Long-term Liabilities	(314)	(330)
Total Liabilities	(5,273)	(3,850)
Shareholders' Equity:
Common Stock, $1 Par Value	(181)	(181)
Other Capital	(5,096)	(5,095)
Retained Earnings	(20,933)	(15,994)
Accumulated Other Comprehensive Loss	5	19
Noncontrolling Minority Interest	0	0
Total Shareholders' Equity	(26,205)	(21,251)
Total Liabilities and Shareholders' Equity	(31,478)	(25,101)
Eliminations and Other | Investments in Conrail
Current Assets:
Investment in Affiliates, Subsidiaries and Other	907	840
Eliminations and Other | Affiliates and Other Companies
Current Assets:
Investment in Affiliates, Subsidiaries and Other	18	15
Eliminations and Other | Investment in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates, Subsidiaries and Other	(29,405)	(24,179)
CSX Corporation
Current Assets:
Cash and Cash Equivalents	274	305	444	510
Short-term Investments	0	415
Accounts Receivable - Net	(1)	2
Receivable from Affiliates	1,226	1,157
Materials and Supplies	0	0
Other Current Assets	(1)	0
Total Current Assets	1,498	1,879
Properties	1	1
Accumulated Depreciation	(1)	(1)
Properties - Net	0	0
Other Long-term Assets	39	2
Total Assets	30,903	26,021
Current Liabilities:
Accounts Payable	105	95
Labor and Fringe Benefits Payable	52	40
Payable to Affiliates	4,792	3,457
Casualty, Environmental and Other Reserves	0	0
Current Maturities of Long-term Debt	0	313
Income and Other Taxes Payable	(326)	(346)
Other Current Liabilities	5	0
Total Current Liabilities	4,628	3,559
Casualty, Environmental and Other Reserves	0	0
Long-term Debt	11,056	10,203
Deferred Income Taxes - Net	(130)	(203)
Other Long-term Liabilities	644	783
Total Liabilities	16,198	14,342
Shareholders' Equity:
Common Stock, $1 Par Value	890	928
Other Capital	217	138
Retained Earnings	14,084	11,253
Accumulated Other Comprehensive Loss	(486)	(640)
Noncontrolling Minority Interest	0	0
Total Shareholders' Equity	14,705	11,679
Total Liabilities and Shareholders' Equity	30,903	26,021
CSX Corporation | Investments in Conrail
Current Assets:
Investment in Affiliates, Subsidiaries and Other	0	0
CSX Corporation | Affiliates and Other Companies
Current Assets:
Investment in Affiliates, Subsidiaries and Other	(39)	(39)
CSX Corporation | Investment in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates, Subsidiaries and Other	29,405	24,179
CSX Transportation
Current Assets:
Cash and Cash Equivalents	121	281	$ 175	$ 100
Short-term Investments	0	0
Accounts Receivable - Net	301	215
Receivable from Affiliates	3,517	2,351
Materials and Supplies	372	407
Other Current Assets	145	106
Total Current Assets	4,456	3,360
Properties	41,479	40,518
Accumulated Depreciation	(11,017)	(10,634)
Properties - Net	30,462	29,884
Other Long-term Assets	596	607
Total Assets	36,314	34,494
Current Liabilities:
Accounts Payable	708	678
Labor and Fringe Benefits Payable	494	440
Payable to Affiliates	552	500
Casualty, Environmental and Other Reserves	95	102
Current Maturities of Long-term Debt	19	19
Income and Other Taxes Payable	455	459
Other Current Liabilities	153	112
Total Current Liabilities	2,476	2,310
Casualty, Environmental and Other Reserves	222	208
Long-term Debt	733	759
Deferred Income Taxes - Net	6,342	9,541
Other Long-term Liabilities	320	410
Total Liabilities	10,093	13,228
Shareholders' Equity:
Common Stock, $1 Par Value	181	181
Other Capital	5,096	5,095
Retained Earnings	20,933	15,994
Accumulated Other Comprehensive Loss	(5)	(19)
Noncontrolling Minority Interest	16	15
Total Shareholders' Equity	26,221	21,266
Total Liabilities and Shareholders' Equity	36,314	34,494
CSX Transportation | Investments in Conrail
Current Assets:
Investment in Affiliates, Subsidiaries and Other	0	0
CSX Transportation | Affiliates and Other Companies
Current Assets:
Investment in Affiliates, Subsidiaries and Other	800	643
CSX Transportation | Investment in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates, Subsidiaries and Other	$ 0	$ 0