Summarized Consolidating Financial Data - Consolidating Balance Sheet (Details) - USD ($) $ / shares in Units, $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 30, 2016
Current Assets:
Cash and Cash Equivalents	$ 1,980	$ 401	$ 930	$ 603
Short-term Investments	10	18
Accounts Receivable - Net	1,045	970
Receivable from Affiliates	0	0
Materials and Supplies	369	372
Other Current Assets	138	154
Total Current Assets	3,542	1,915
Properties	44,103	44,324
Accumulated Depreciation	(12,355)	(12,560)
Properties - Net	31,748	31,764
Other Long-term Assets	435	374
Total Assets	37,439	35,739
Current Liabilities:
Accounts Payable	905	847
Labor and Fringe Benefits Payable	443	602
Payable to Affiliates	0	0
Casualty, Environmental and Other Reserves	106	108
Current Maturities of Long-term Debt	19	19
Income and Other Taxes Payable	274	157
Other Current Liabilities	144	161
Total Current Liabilities	1,891	1,894
Casualty, Environmental and Other Reserves	258	266
Long-term Debt	13,768	11,790
Deferred Income Taxes - Net	6,485	6,418
Other Long-term Liabilities	646	650
Total Liabilities	23,048	21,018
Shareholders' Equity
Common Stock, $1 Par Value	875	890
Other Capital	215	217
Retained Earnings	13,873	14,084
Accumulated Other Comprehensive Loss	(585)	(486)
Noncontrolling Interest	13	16
Total Shareholders' Equity	14,391	14,721
Total Liabilities and Shareholders' Equity	$ 37,439	$ 35,739
Common stock, par value (in dollars per share)	$ 1	$ 1
Investments in Conrail
Current Assets:
Investment in Affiliates and Other Companies	$ 918	$ 907
Affiliates and Other Companies
Current Assets:
Investment in Affiliates and Other Companies	796	779
Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Other Companies	0	0
Eliminations and Other
Current Assets:
Cash and Cash Equivalents	5	6	10	17
Short-term Investments	10	18
Accounts Receivable - Net	790	670
Receivable from Affiliates	(4,638)	(4,743)
Materials and Supplies	0	0
Other Current Assets	12	10
Total Current Assets	(3,821)	(4,039)
Properties	2,872	2,844
Accumulated Depreciation	(1,582)	(1,542)
Properties - Net	1,290	1,302
Other Long-term Assets	(246)	(261)
Total Assets	(31,756)	(31,478)
Current Liabilities:
Accounts Payable	36	34
Labor and Fringe Benefits Payable	22	56
Payable to Affiliates	(5,129)	(5,344)
Casualty, Environmental and Other Reserves	13	13
Current Maturities of Long-term Debt	1	0
Income and Other Taxes Payable	19	28
Other Current Liabilities	0	3
Total Current Liabilities	(5,038)	(5,210)
Casualty, Environmental and Other Reserves	43	44
Long-term Debt	0	1
Deferred Income Taxes - Net	209	206
Other Long-term Liabilities	(309)	(314)
Total Liabilities	(5,095)	(5,273)
Shareholders' Equity
Common Stock, $1 Par Value	(181)	(181)
Other Capital	(5,097)	(5,096)
Retained Earnings	(21,392)	(20,933)
Accumulated Other Comprehensive Loss	9	5
Noncontrolling Interest	0	0
Total Shareholders' Equity	(26,661)	(26,205)
Total Liabilities and Shareholders' Equity	(31,756)	(31,478)
Eliminations and Other | Investments in Conrail
Current Assets:
Investment in Affiliates and Other Companies	918	907
Eliminations and Other | Affiliates and Other Companies
Current Assets:
Investment in Affiliates and Other Companies	18	18
Eliminations and Other | Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Other Companies	(29,915)	(29,405)
CSX Corporation
Current Assets:
Cash and Cash Equivalents	1,894	274	648	305
Short-term Investments	0	0
Accounts Receivable - Net	2	(1)
Receivable from Affiliates	991	1,226
Materials and Supplies	0	0
Other Current Assets	(1)	(1)
Total Current Assets	2,886	1,498
Properties	1	1
Accumulated Depreciation	(1)	(1)
Properties - Net	0	0
Other Long-term Assets	52	39
Total Assets	32,814	30,903
Current Liabilities:
Accounts Payable	195	105
Labor and Fringe Benefits Payable	37	52
Payable to Affiliates	4,763	4,792
Casualty, Environmental and Other Reserves	0	0
Current Maturities of Long-term Debt	0	0
Income and Other Taxes Payable	(126)	(326)
Other Current Liabilities	2	5
Total Current Liabilities	4,871	4,628
Casualty, Environmental and Other Reserves	0	0
Long-term Debt	13,036	11,056
Deferred Income Taxes - Net	(113)	(130)
Other Long-term Liabilities	642	644
Total Liabilities	18,436	16,198
Shareholders' Equity
Common Stock, $1 Par Value	875	890
Other Capital	215	217
Retained Earnings	13,873	14,084
Accumulated Other Comprehensive Loss	(585)	(486)
Noncontrolling Interest	0	0
Total Shareholders' Equity	14,378	14,705
Total Liabilities and Shareholders' Equity	32,814	30,903
CSX Corporation | Investments in Conrail
Current Assets:
Investment in Affiliates and Other Companies	0	0
CSX Corporation | Affiliates and Other Companies
Current Assets:
Investment in Affiliates and Other Companies	(39)	(39)
CSX Corporation | Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Other Companies	29,915	29,405
CSX Transportation
Current Assets:
Cash and Cash Equivalents	81	121	$ 272	$ 281
Short-term Investments	0	0
Accounts Receivable - Net	253	301
Receivable from Affiliates	3,647	3,517
Materials and Supplies	369	372
Other Current Assets	127	145
Total Current Assets	4,477	4,456
Properties	41,230	41,479
Accumulated Depreciation	(10,772)	(11,017)
Properties - Net	30,458	30,462
Other Long-term Assets	629	596
Total Assets	36,381	36,314
Current Liabilities:
Accounts Payable	674	708
Labor and Fringe Benefits Payable	384	494
Payable to Affiliates	366	552
Casualty, Environmental and Other Reserves	93	95
Current Maturities of Long-term Debt	18	19
Income and Other Taxes Payable	381	455
Other Current Liabilities	142	153
Total Current Liabilities	2,058	2,476
Casualty, Environmental and Other Reserves	215	222
Long-term Debt	732	733
Deferred Income Taxes - Net	6,389	6,342
Other Long-term Liabilities	313	320
Total Liabilities	9,707	10,093
Shareholders' Equity
Common Stock, $1 Par Value	181	181
Other Capital	5,097	5,096
Retained Earnings	21,392	20,933
Accumulated Other Comprehensive Loss	(9)	(5)
Noncontrolling Interest	13	16
Total Shareholders' Equity	26,674	26,221
Total Liabilities and Shareholders' Equity	36,381	36,314
CSX Transportation | Investments in Conrail
Current Assets:
Investment in Affiliates and Other Companies	0	0
CSX Transportation | Affiliates and Other Companies
Current Assets:
Investment in Affiliates and Other Companies	817	800
CSX Transportation | Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Other Companies	$ 0	$ 0