Summarized Consolidating Financial Data - Consolidating Balance Sheet (Details) - USD ($) $ / shares in Units, $ in Millions	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Current Assets:
Cash and Cash Equivalents	$ 1,188	$ 858	$ 1,980	$ 401
Short-term Investments	822	253
Accounts Receivable - Net	1,106	1,010
Receivable from Affiliates	0	0
Materials and Supplies	241	263
Other Current Assets	122	181
Total Current Assets	3,479	2,565
Properties	44,826	44,805
Accumulated Depreciation	(12,838)	(12,807)
Properties - Net	31,988	31,998
Right-of-Use Lease Asset	550	0
Other Long-term Assets	344	387
Total Assets	38,154	36,729
Current Liabilities:
Accounts Payable	1,019	949
Labor and Fringe Benefits Payable	406	550
Payable to Affiliates	0	0
Casualty, Environmental and Other Reserves	112	113
Current Maturities of Long-term Debt	18	18
Income and Other Taxes Payable	193	106
Other Current Liabilities	178	179
Total Current Liabilities	1,926	1,915
Casualty, Environmental and Other Reserves	207	211
Long-term Debt	15,748	14,739
Deferred Income Taxes - Net	6,743	6,690
Long-term lease liabilities	502	0
Other Long-term Liabilities	583	594
Total Liabilities	25,709	24,149
Shareholders' Equity
Common Stock, $1 Par Value	809	818
Other Capital	267	249
Retained Earnings	12,011	12,157
Accumulated Other Comprehensive Loss	(659)	(661)
Noncontrolling Interest	17	17
Total Shareholders' Equity	12,445	12,580	14,391	14,721
Total Liabilities and Shareholders' Equity	$ 38,154	$ 36,729
Common stock, par value (in dollars per share)	$ 1	$ 1
Investments in Conrail
Current Assets:
Investment in Affiliates and Other Companies	$ 948	$ 943
Affiliates and Other Companies
Current Assets:
Investment in Affiliates and Other Companies	845	836
Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Other Companies	0	0
Eliminations and Other
Current Assets:
Cash and Cash Equivalents	13	12	5	6
Short-term Investments	9	3
Accounts Receivable - Net	48	6
Receivable from Affiliates	(6,520)	(6,234)
Materials and Supplies	0	0
Other Current Assets	13	14
Total Current Assets	(6,437)	(6,199)
Properties	2,929	2,907
Accumulated Depreciation	(1,646)	(1,612)
Properties - Net	1,283	1,295
Right-of-Use Lease Asset	22
Other Long-term Assets	(252)	(213)
Total Assets	(37,076)	(36,191)
Current Liabilities:
Accounts Payable	44	54
Labor and Fringe Benefits Payable	25	69
Payable to Affiliates	(7,917)	(7,606)
Casualty, Environmental and Other Reserves	14	14
Current Maturities of Long-term Debt	0	0
Income and Other Taxes Payable	24	4
Other Current Liabilities	12	6
Total Current Liabilities	(7,798)	(7,459)
Casualty, Environmental and Other Reserves	35	35
Long-term Debt	0	0
Deferred Income Taxes - Net	227	223
Long-term lease liabilities	15
Other Long-term Liabilities	(334)	(338)
Total Liabilities	(7,855)	(7,539)
Shareholders' Equity
Common Stock, $1 Par Value	(181)	(181)
Other Capital	(5,096)	(5,096)
Retained Earnings	(23,893)	(23,322)
Accumulated Other Comprehensive Loss	(51)	(53)
Noncontrolling Interest	0	0
Total Shareholders' Equity	(29,221)	(28,652)
Total Liabilities and Shareholders' Equity	(37,076)	(36,191)
Eliminations and Other | Investments in Conrail
Current Assets:
Investment in Affiliates and Other Companies	948	943
Eliminations and Other | Affiliates and Other Companies
Current Assets:
Investment in Affiliates and Other Companies	16	16
Eliminations and Other | Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Other Companies	(32,656)	(32,033)
CSX Corporation
Current Assets:
Cash and Cash Equivalents	1,032	716	1,894	274
CSX Corporation | Corporate, Non-Segment
Current Assets:
Cash and Cash Equivalents	1,032	716
Short-term Investments	813	250
Accounts Receivable - Net	0	1
Receivable from Affiliates	1,022	1,020
Materials and Supplies	0	0
Other Current Assets	0	63
Total Current Assets	2,867	2,050
Properties	1	1
Accumulated Depreciation	(1)	(1)
Properties - Net	0	0
Right-of-Use Lease Asset	0
Other Long-term Assets	0	2
Total Assets	35,484	34,046
Current Liabilities:
Accounts Payable	202	132
Labor and Fringe Benefits Payable	33	41
Payable to Affiliates	7,480	6,973
Casualty, Environmental and Other Reserves	0	0
Current Maturities of Long-term Debt	0	0
Income and Other Taxes Payable	(275)	(290)
Other Current Liabilities	1	11
Total Current Liabilities	7,441	6,867
Casualty, Environmental and Other Reserves	0	0
Long-term Debt	15,040	14,029
Deferred Income Taxes - Net	(129)	(134)
Long-term lease liabilities	0
Other Long-term Liabilities	704	721
Total Liabilities	23,056	21,483
Shareholders' Equity
Common Stock, $1 Par Value	809	818
Other Capital	267	249
Retained Earnings	12,011	12,157
Accumulated Other Comprehensive Loss	(659)	(661)
Noncontrolling Interest	0	0
Total Shareholders' Equity	12,428	12,563
Total Liabilities and Shareholders' Equity	35,484	34,046
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	32,656	32,033
CSX Transportation
Current Assets:
Cash and Cash Equivalents	143	130	$ 81	$ 121
Short-term Investments	0	0
Accounts Receivable - Net	1,058	1,003
Receivable from Affiliates	5,498	5,214
Materials and Supplies	241	263
Other Current Assets	109	104
Total Current Assets	7,049	6,714
Properties	41,896	41,897
Accumulated Depreciation	(11,191)	(11,194)
Properties - Net	30,705	30,703
Right-of-Use Lease Asset	528
Other Long-term Assets	596	598
Total Assets	39,746	38,874
Current Liabilities:
Accounts Payable	773	763
Labor and Fringe Benefits Payable	348	440
Payable to Affiliates	437	633
Casualty, Environmental and Other Reserves	98	99
Current Maturities of Long-term Debt	18	18
Income and Other Taxes Payable	444	392
Other Current Liabilities	165	162
Total Current Liabilities	2,283	2,507
Casualty, Environmental and Other Reserves	172	176
Long-term Debt	708	710
Deferred Income Taxes - Net	6,645	6,601
Long-term lease liabilities	487
Other Long-term Liabilities	213	211
Total Liabilities	10,508	10,205
Shareholders' Equity
Common Stock, $1 Par Value	181	181
Other Capital	5,096	5,096
Retained Earnings	23,893	23,322
Accumulated Other Comprehensive Loss	51	53
Noncontrolling Interest	17	17
Total Shareholders' Equity	29,238	28,669
Total Liabilities and Shareholders' Equity	39,746	38,874
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	868	859
CSX Transportation | Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Other Companies	$ 0	$ 0