Summarized Consolidating Financial Data (Consolidating Balance Sheets) (Details) - USD ($) $ / shares in Units, $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 30, 2016	Dec. 25, 2015
Current Assets:
Cash and Cash Equivalents	$ 858	$ 401	$ 603	$ 628
Short-term Investments	253	18
Accounts Receivable - Net	1,010	970
Receivable from Affiliates	0	0
Materials and Supplies	263	372
Other Current Assets	181	154
Total Current Assets	2,565	1,915
Properties	44,805	44,324
Accumulated Depreciation	(12,807)	(12,560)
Properties - Net	31,998	31,764
Other Long-term Assets	387	374
Total Assets	36,729	35,739
Current Liabilities:
Accounts Payable	949	847
Labor and Fringe Benefits Payable	550	602
Payable to Affiliates	0	0
Casualty, Environmental and Other Reserves	113	108
Current Maturities of Long-term Debt	18	19
Income and Other Taxes Payable	106	157
Other Current Liabilities	179	161
Total Current Liabilities	1,915	1,894
Casualty, Environmental and Other Reserves	211	266
Long-term Debt	14,739	11,790
Deferred Income Taxes - Net	6,690	6,418
Other Long-term Liabilities	594	650
Total Liabilities	24,149	21,018
Shareholders' Equity:
Common Stock, $1 Par Value	818	890
Other Capital	249	217
Retained Earnings	12,157	14,084
Accumulated Other Comprehensive Loss	(661)	(486)
Noncontrolling Minority Interest	17	16
Total Shareholders' Equity	12,580	14,721	11,694	11,668
Total Liabilities and Shareholders' Equity	$ 36,729	$ 35,739
Common stock par value (in dollars per share)	$ 1.00	$ 1.00
Investments in Conrail
Current Assets:
Investment in Affiliates and Other Companies	$ 943	$ 907
Affiliates and Other Companies
Current Assets:
Investment in Affiliates and Other Companies	836	779
Investment in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Other Companies	0	0
Eliminations and Other
Current Assets:
Cash and Cash Equivalents	12	6	17	9
Short-term Investments	3	18
Accounts Receivable - Net	6	670
Receivable from Affiliates	(6,234)	(4,743)
Materials and Supplies	0	0
Other Current Assets	14	10
Total Current Assets	(6,199)	(4,039)
Properties	2,907	2,844
Accumulated Depreciation	(1,612)	(1,542)
Properties - Net	1,295	1,302
Other Long-term Assets	(213)	(261)
Total Assets	(36,191)	(31,478)
Current Liabilities:
Accounts Payable	54	34
Labor and Fringe Benefits Payable	69	56
Payable to Affiliates	(7,606)	(5,344)
Casualty, Environmental and Other Reserves	14	13
Current Maturities of Long-term Debt	0	0
Income and Other Taxes Payable	4	28
Other Current Liabilities	6	3
Total Current Liabilities	(7,459)	(5,210)
Casualty, Environmental and Other Reserves	35	44
Long-term Debt	0	1
Deferred Income Taxes - Net	223	206
Other Long-term Liabilities	(338)	(314)
Total Liabilities	(7,539)	(5,273)
Shareholders' Equity:
Common Stock, $1 Par Value	(181)	(181)
Other Capital	(5,096)	(5,096)
Retained Earnings	(23,322)	(20,933)
Accumulated Other Comprehensive Loss	(53)	5
Noncontrolling Minority Interest	0	0
Total Shareholders' Equity	(28,652)	(26,205)
Total Liabilities and Shareholders' Equity	(36,191)	(31,478)
Eliminations and Other | Investments in Conrail
Current Assets:
Investment in Affiliates and Other Companies	943	907
Eliminations and Other | Affiliates and Other Companies
Current Assets:
Investment in Affiliates and Other Companies	16	18
Eliminations and Other | Investment in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Other Companies	(32,033)	(29,405)
CSX Corporation
Current Assets:
Cash and Cash Equivalents	716	274	305	444
Short-term Investments	250	0
Accounts Receivable - Net	1	(1)
Receivable from Affiliates	1,020	1,226
Materials and Supplies	0	0
Other Current Assets	63	(1)
Total Current Assets	2,050	1,498
Properties	1	1
Accumulated Depreciation	(1)	(1)
Properties - Net	0	0
Other Long-term Assets	2	39
Total Assets	34,046	30,903
Current Liabilities:
Accounts Payable	132	105
Labor and Fringe Benefits Payable	41	52
Payable to Affiliates	6,973	4,792
Casualty, Environmental and Other Reserves	0	0
Current Maturities of Long-term Debt	0	0
Income and Other Taxes Payable	(290)	(326)
Other Current Liabilities	11	5
Total Current Liabilities	6,867	4,628
Casualty, Environmental and Other Reserves	0	0
Long-term Debt	14,029	11,056
Deferred Income Taxes - Net	(134)	(130)
Other Long-term Liabilities	721	644
Total Liabilities	21,483	16,198
Shareholders' Equity:
Common Stock, $1 Par Value	818	890
Other Capital	249	217
Retained Earnings	12,157	14,084
Accumulated Other Comprehensive Loss	(661)	(486)
Noncontrolling Minority Interest	0	0
Total Shareholders' Equity	12,563	14,705
Total Liabilities and Shareholders' Equity	34,046	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 | Investment in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Other Companies	32,033	29,405
CSX Transportation
Current Assets:
Cash and Cash Equivalents	130	121	$ 281	$ 175
Short-term Investments	0	0
Accounts Receivable - Net	1,003	301
Receivable from Affiliates	5,214	3,517
Materials and Supplies	263	372
Other Current Assets	104	145
Total Current Assets	6,714	4,456
Properties	41,897	41,479
Accumulated Depreciation	(11,194)	(11,017)
Properties - Net	30,703	30,462
Other Long-term Assets	598	596
Total Assets	38,874	36,314
Current Liabilities:
Accounts Payable	763	708
Labor and Fringe Benefits Payable	440	494
Payable to Affiliates	633	552
Casualty, Environmental and Other Reserves	99	95
Current Maturities of Long-term Debt	18	19
Income and Other Taxes Payable	392	455
Other Current Liabilities	162	153
Total Current Liabilities	2,507	2,476
Casualty, Environmental and Other Reserves	176	222
Long-term Debt	710	733
Deferred Income Taxes - Net	6,601	6,342
Other Long-term Liabilities	211	320
Total Liabilities	10,205	10,093
Shareholders' Equity:
Common Stock, $1 Par Value	181	181
Other Capital	5,096	5,096
Retained Earnings	23,322	20,933
Accumulated Other Comprehensive Loss	53	(5)
Noncontrolling Minority Interest	17	16
Total Shareholders' Equity	28,669	26,221
Total Liabilities and Shareholders' Equity	38,874	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	859	800
CSX Transportation | Investment in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Other Companies	$ 0	$ 0