Summarized Consolidating Financial Data - Consolidating Balance Sheet (Details) - USD ($) $ / shares in Units, $ in Millions	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 30, 2016
Current Assets:
Cash and Cash Equivalents	$ 1,320	$ 401	$ 620	$ 603
Short-term Investments	83	18
Accounts Receivable - Net	1,036	970
Receivable from Affiliates	0	0
Materials and Supplies	326	372
Other Current Assets	116	154
Total Current Assets	2,881	1,915
Properties	44,306	44,324
Accumulated Depreciation	(12,459)	(12,560)
Properties - Net	31,847	31,764
Other Long-term Assets	455	374
Total Assets	36,924	35,739
Current Liabilities:
Accounts Payable	852	847
Labor and Fringe Benefits Payable	486	602
Payable to Affiliates	0	0
Casualty, Environmental and Other Reserves	114	108
Current Maturities of Long-term Debt	19	19
Income and Other Taxes Payable	123	157
Other Current Liabilities	138	161
Total Current Liabilities	1,732	1,894
Casualty, Environmental and Other Reserves	232	266
Long-term Debt	13,769	11,790
Deferred Income Taxes - Net	6,532	6,418
Other Long-term Liabilities	636	650
Total Liabilities	22,901	21,018
Shareholders' Equity
Common Stock, $1 Par Value	859	890
Other Capital	127	217
Retained Earnings	13,604	14,084
Accumulated Other Comprehensive Loss	(581)	(486)
Noncontrolling Interest	14	16
Total Shareholders' Equity	14,023	14,721
Total Liabilities and Shareholders' Equity	$ 36,924	$ 35,739
Common stock, par value (in dollars per share)	$ 1	$ 1
Investments in Conrail
Current Assets:
Investment in Affiliates and Other Companies	$ 931	$ 907
Affiliates and Other Companies
Current Assets:
Investment in Affiliates and Other Companies	810	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	9	17
Short-term Investments	8	18
Accounts Receivable - Net	771	670
Receivable from Affiliates	(5,365)	(4,743)
Materials and Supplies	0	0
Other Current Assets	18	10
Total Current Assets	(4,563)	(4,039)
Properties	2,813	2,844
Accumulated Depreciation	(1,530)	(1,542)
Properties - Net	1,283	1,302
Other Long-term Assets	(240)	(261)
Total Assets	(33,157)	(31,478)
Current Liabilities:
Accounts Payable	49	34
Labor and Fringe Benefits Payable	67	56
Payable to Affiliates	(5,977)	(5,344)
Casualty, Environmental and Other Reserves	13	13
Current Maturities of Long-term Debt	1	0
Income and Other Taxes Payable	32	28
Other Current Liabilities	10	3
Total Current Liabilities	(5,805)	(5,210)
Casualty, Environmental and Other Reserves	42	44
Long-term Debt	0	1
Deferred Income Taxes - Net	205	206
Other Long-term Liabilities	(307)	(314)
Total Liabilities	(5,865)	(5,273)
Shareholders' Equity
Common Stock, $1 Par Value	(181)	(181)
Other Capital	(5,096)	(5,096)
Retained Earnings	(22,025)	(20,933)
Accumulated Other Comprehensive Loss	10	5
Noncontrolling Interest	0	0
Total Shareholders' Equity	(27,292)	(26,205)
Total Liabilities and Shareholders' Equity	(33,157)	(31,478)
Eliminations and Other | Investments in Conrail
Current Assets:
Investment in Affiliates and Other Companies	931	907
Eliminations and Other | Affiliates and Other Companies
Current Assets:
Investment in Affiliates and Other Companies	17	18
Eliminations and Other | Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Other Companies	(30,585)	(29,405)
CSX Corporation
Current Assets:
Cash and Cash Equivalents	1,172	274	483	305
CSX Corporation | Corporate, Non-Segment
Current Assets:
Cash and Cash Equivalents	1,172	274
Short-term Investments	75	0
Accounts Receivable - Net	(6)	(1)
Receivable from Affiliates	1,005	1,226
Materials and Supplies	0	0
Other Current Assets	0	(1)
Total Current Assets	2,246	1,498
Properties	1	1
Accumulated Depreciation	(1)	(1)
Properties - Net	0	0
Other Long-term Assets	65	39
Total Assets	32,857	30,903
Current Liabilities:
Accounts Payable	93	105
Labor and Fringe Benefits Payable	38	52
Payable to Affiliates	5,536	4,792
Casualty, Environmental and Other Reserves	0	0
Current Maturities of Long-term Debt	0	0
Income and Other Taxes Payable	(389)	(326)
Other Current Liabilities	2	5
Total Current Liabilities	5,280	4,628
Casualty, Environmental and Other Reserves	0	0
Long-term Debt	13,039	11,056
Deferred Income Taxes - Net	(109)	(130)
Other Long-term Liabilities	638	644
Total Liabilities	18,848	16,198
Shareholders' Equity
Common Stock, $1 Par Value	859	890
Other Capital	127	217
Retained Earnings	13,604	14,084
Accumulated Other Comprehensive Loss	(581)	(486)
Noncontrolling Interest	0	0
Total Shareholders' Equity	14,009	14,705
Total Liabilities and Shareholders' Equity	32,857	30,903
CSX Corporation | Corporate, Non-Segment | Investments in Conrail
Current Assets:
Investment in Affiliates and Other Companies	0	0
CSX Corporation | Corporate, Non-Segment | Affiliates and Other Companies
Current Assets:
Investment in Affiliates and Other Companies	(39)	(39)
CSX Corporation | Corporate, Non-Segment | Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Other Companies	30,585	29,405
CSX Transportation
Current Assets:
Cash and Cash Equivalents	143	121	$ 128	$ 281
Short-term Investments	0	0
Accounts Receivable - Net	271	301
Receivable from Affiliates	4,360	3,517
Materials and Supplies	326	372
Other Current Assets	98	145
Total Current Assets	5,198	4,456
Properties	41,492	41,479
Accumulated Depreciation	(10,928)	(11,017)
Properties - Net	30,564	30,462
Other Long-term Assets	630	596
Total Assets	37,224	36,314
Current Liabilities:
Accounts Payable	710	708
Labor and Fringe Benefits Payable	381	494
Payable to Affiliates	441	552
Casualty, Environmental and Other Reserves	101	95
Current Maturities of Long-term Debt	18	19
Income and Other Taxes Payable	480	455
Other Current Liabilities	126	153
Total Current Liabilities	2,257	2,476
Casualty, Environmental and Other Reserves	190	222
Long-term Debt	730	733
Deferred Income Taxes - Net	6,436	6,342
Other Long-term Liabilities	305	320
Total Liabilities	9,918	10,093
Shareholders' Equity
Common Stock, $1 Par Value	181	181
Other Capital	5,096	5,096
Retained Earnings	22,025	20,933
Accumulated Other Comprehensive Loss	(10)	(5)
Noncontrolling Interest	14	16
Total Shareholders' Equity	27,306	26,221
Total Liabilities and Shareholders' Equity	37,224	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	832	800
CSX Transportation | Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Other Companies	$ 0	$ 0