Summarized Consolidating Financial Data - Consolidating Balance Sheet (Details) - USD ($) $ / shares in Units, $ in Millions	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 30, 2016
Current Assets:
Cash and Cash Equivalents	$ 663	$ 401	$ 591	$ 603
Short-term Investments	615	18
Accounts Receivable - Net	1,090	970
Receivable from Affiliates	0	0
Materials and Supplies	283	372
Other Current Assets	133	154
Total Current Assets	2,784	1,915
Properties	44,485	44,324
Accumulated Depreciation	(12,614)	(12,560)
Properties - Net	31,871	31,764
Other Long-term Assets	442	374
Total Assets	36,861	35,739
Current Liabilities:
Accounts Payable	982	847
Labor and Fringe Benefits Payable	517	602
Payable to Affiliates	0	0
Casualty, Environmental and Other Reserves	110	108
Current Maturities of Long-term Debt	18	19
Income and Other Taxes Payable	166	157
Other Current Liabilities	151	161
Total Current Liabilities	1,944	1,894
Casualty, Environmental and Other Reserves	231	266
Long-term Debt	13,754	11,790
Deferred Income Taxes - Net	6,584	6,418
Other Long-term Liabilities	613	650
Total Liabilities	23,126	21,018
Shareholders' Equity
Common Stock, $1 Par Value	844	890
Other Capital	129	217
Retained Earnings	13,320	14,084
Accumulated Other Comprehensive Loss	(574)	(486)
Noncontrolling Interest	16	16
Total Shareholders' Equity	13,735	14,721
Total Liabilities and Shareholders' Equity	$ 36,861	$ 35,739
Common stock, par value (in dollars per share)	$ 1	$ 1
Investments in Conrail
Current Assets:
Investment in Affiliates and Other Companies	$ 941	$ 907
Affiliates and Other Companies
Current Assets:
Investment in Affiliates and Other Companies	823	779
Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Other Companies	0	0
Eliminations and Other
Current Assets:
Cash and Cash Equivalents	10	6	11	17
Short-term Investments	5	18
Accounts Receivable - Net	868	670
Receivable from Affiliates	(6,216)	(4,743)
Materials and Supplies	0	0
Other Current Assets	18	10
Total Current Assets	(5,315)	(4,039)
Properties	2,855	2,844
Accumulated Depreciation	(1,570)	(1,542)
Properties - Net	1,285	1,302
Other Long-term Assets	(248)	(261)
Total Assets	(34,609)	(31,478)
Current Liabilities:
Accounts Payable	40	34
Labor and Fringe Benefits Payable	43	56
Payable to Affiliates	(6,736)	(5,344)
Casualty, Environmental and Other Reserves	13	13
Current Maturities of Long-term Debt	0	0
Income and Other Taxes Payable	39	28
Other Current Liabilities	2	3
Total Current Liabilities	(6,599)	(5,210)
Casualty, Environmental and Other Reserves	40	44
Long-term Debt	0	1
Deferred Income Taxes - Net	199	206
Other Long-term Liabilities	(304)	(314)
Total Liabilities	(6,664)	(5,273)
Shareholders' Equity
Common Stock, $1 Par Value	(181)	(181)
Other Capital	(5,096)	(5,096)
Retained Earnings	(22,679)	(20,933)
Accumulated Other Comprehensive Loss	11	5
Noncontrolling Interest	0	0
Total Shareholders' Equity	(27,945)	(26,205)
Total Liabilities and Shareholders' Equity	(34,609)	(31,478)
Eliminations and Other | Investments in Conrail
Current Assets:
Investment in Affiliates and Other Companies	941	907
Eliminations and Other | Affiliates and Other Companies
Current Assets:
Investment in Affiliates and Other Companies	16	18
Eliminations and Other | Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Other Companies	(31,288)	(29,405)
CSX Corporation
Current Assets:
Cash and Cash Equivalents	537	274	433	305
CSX Corporation | Corporate, Non-Segment
Current Assets:
Cash and Cash Equivalents	537	274
Short-term Investments	610	0
Accounts Receivable - Net	1	(1)
Receivable from Affiliates	960	1,226
Materials and Supplies	0	0
Other Current Assets	0	(1)
Total Current Assets	2,108	1,498
Properties	1	1
Accumulated Depreciation	(1)	(1)
Properties - Net	0	0
Other Long-term Assets	77	39
Total Assets	33,434	30,903
Current Liabilities:
Accounts Payable	189	105
Labor and Fringe Benefits Payable	40	52
Payable to Affiliates	6,339	4,792
Casualty, Environmental and Other Reserves	0	0
Current Maturities of Long-term Debt	0	0
Income and Other Taxes Payable	(415)	(326)
Other Current Liabilities	1	5
Total Current Liabilities	6,154	4,628
Casualty, Environmental and Other Reserves	0	0
Long-term Debt	13,043	11,056
Deferred Income Taxes - Net	(99)	(130)
Other Long-term Liabilities	617	644
Total Liabilities	19,715	16,198
Shareholders' Equity
Common Stock, $1 Par Value	844	890
Other Capital	129	217
Retained Earnings	13,320	14,084
Accumulated Other Comprehensive Loss	(574)	(486)
Noncontrolling Interest	0	0
Total Shareholders' Equity	13,719	14,705
Total Liabilities and Shareholders' Equity	33,434	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	31,288	29,405
CSX Transportation
Current Assets:
Cash and Cash Equivalents	116	121	$ 147	$ 281
Short-term Investments	0	0
Accounts Receivable - Net	221	301
Receivable from Affiliates	5,256	3,517
Materials and Supplies	283	372
Other Current Assets	115	145
Total Current Assets	5,991	4,456
Properties	41,629	41,479
Accumulated Depreciation	(11,043)	(11,017)
Properties - Net	30,586	30,462
Other Long-term Assets	613	596
Total Assets	38,036	36,314
Current Liabilities:
Accounts Payable	753	708
Labor and Fringe Benefits Payable	434	494
Payable to Affiliates	397	552
Casualty, Environmental and Other Reserves	97	95
Current Maturities of Long-term Debt	18	19
Income and Other Taxes Payable	542	455
Other Current Liabilities	148	153
Total Current Liabilities	2,389	2,476
Casualty, Environmental and Other Reserves	191	222
Long-term Debt	711	733
Deferred Income Taxes - Net	6,484	6,342
Other Long-term Liabilities	300	320
Total Liabilities	10,075	10,093
Shareholders' Equity
Common Stock, $1 Par Value	181	181
Other Capital	5,096	5,096
Retained Earnings	22,679	20,933
Accumulated Other Comprehensive Loss	(11)	(5)
Noncontrolling Interest	16	16
Total Shareholders' Equity	27,961	26,221
Total Liabilities and Shareholders' Equity	38,036	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	846	800
CSX Transportation | Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Other Companies	$ 0	$ 0