Summarized Consolidating Financial Data - Consolidating Balance Sheet (Details) - USD ($) $ / shares in Units, $ in Millions	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Current Assets:
Cash and Cash Equivalents	$ 1,521			$ 858	$ 663			$ 401
Short-term Investments	1,037			253
Accounts Receivable - Net	1,101			1,010
Receivable from Affiliates	0			0
Materials and Supplies	235			263
Other Current Assets	66			181
Total Current Assets	3,960			2,565
Properties	45,012			44,805
Accumulated Depreciation	(12,934)			(12,807)
Properties - Net	32,078			31,998
Right-of-Use Lease Asset	539			0
Other Long-term Assets	369			387
Total Assets	38,795			36,729
Current Liabilities:
Accounts Payable	1,101			949
Labor and Fringe Benefits Payable	486			550
Payable to Affiliates	0			0
Casualty, Environmental and Other Reserves	110			113
Current Maturities of Long-term Debt	745			18
Income and Other Taxes Payable	155			106
Other Current Liabilities	208			179
Total Current Liabilities	2,805			1,915
Casualty, Environmental and Other Reserves	195			211
Long-term Debt	15,992			14,739
Deferred Income Taxes - Net	6,882			6,690
Long-term lease liabilities	494			0
Other Long-term Liabilities	548			594
Total Liabilities	26,916			24,149
Shareholders' Equity
Common Stock, $1 Par Value	782			818
Other Capital	314			249
Retained Earnings	11,416			12,157
Accumulated Other Comprehensive Loss	(648)			(661)
Noncontrolling Interest	15			17
Total Shareholders' Equity	11,879	$ 12,290	$ 12,445	12,580	13,735	$ 14,023	$ 14,391	14,721
Total Liabilities and Shareholders' Equity	$ 38,795			$ 36,729
Common stock, par value (in dollars per share)	$ 1			$ 1
Investments in Conrail
Current Assets:
Investment in Affiliates and Other Companies	$ 969			$ 943
Affiliates and Other Companies
Current Assets:
Investment in Affiliates and Other Companies	880			836
Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Other Companies	0			0
Eliminations and Other
Current Assets:
Cash and Cash Equivalents	14			12	10			6
Short-term Investments	9			3
Accounts Receivable - Net	55			6
Receivable from Affiliates	(7,792)			(6,234)
Materials and Supplies	0			0
Other Current Assets	17			14
Total Current Assets	(7,697)			(6,199)
Properties	2,956			2,907
Accumulated Depreciation	(1,702)			(1,612)
Properties - Net	1,254			1,295
Right-of-Use Lease Asset	20
Other Long-term Assets	(242)			(213)
Total Assets	(39,647)			(36,191)
Current Liabilities:
Accounts Payable	69			54
Labor and Fringe Benefits Payable	39			69
Payable to Affiliates	(9,344)			(7,606)
Casualty, Environmental and Other Reserves	15			14
Current Maturities of Long-term Debt	0			0
Income and Other Taxes Payable	13			4
Other Current Liabilities	11			6
Total Current Liabilities	(9,197)			(7,459)
Casualty, Environmental and Other Reserves	34			35
Long-term Debt	0			0
Deferred Income Taxes - Net	277			223
Long-term lease liabilities	13
Other Long-term Liabilities	(330)			(338)
Total Liabilities	(9,203)			(7,539)
Shareholders' Equity
Common Stock, $1 Par Value	(181)			(181)
Other Capital	(5,096)			(5,096)
Retained Earnings	(25,118)			(23,322)
Accumulated Other Comprehensive Loss	(49)			(53)
Noncontrolling Interest	0			0
Total Shareholders' Equity	(30,444)			(28,652)
Total Liabilities and Shareholders' Equity	(39,647)			(36,191)
Eliminations and Other | Investments in Conrail
Current Assets:
Investment in Affiliates and Other Companies	969			943
Eliminations and Other | Affiliates and Other Companies
Current Assets:
Investment in Affiliates and Other Companies	15			16
Eliminations and Other | Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Other Companies	(33,966)			(32,033)
CSX Corporation
Current Assets:
Cash and Cash Equivalents	1,355			716	537			274
CSX Corporation | Corporate, Non-Segment
Current Assets:
Cash and Cash Equivalents	1,355			716
Short-term Investments	1,028			250
Accounts Receivable - Net	2			1
Receivable from Affiliates	874			1,020
Materials and Supplies	0			0
Other Current Assets	(1)			63
Total Current Assets	3,258			2,050
Properties	1			1
Accumulated Depreciation	(1)			(1)
Properties - Net	0			0
Right-of-Use Lease Asset	0
Other Long-term Assets	3			2
Total Assets	37,188			34,046
Current Liabilities:
Accounts Payable	200			132
Labor and Fringe Benefits Payable	36			41
Payable to Affiliates	8,959			6,973
Casualty, Environmental and Other Reserves	0			0
Current Maturities of Long-term Debt	500			0
Income and Other Taxes Payable	(428)			(290)
Other Current Liabilities	0			11
Total Current Liabilities	9,267			6,867
Casualty, Environmental and Other Reserves	0			0
Long-term Debt	15,532			14,029
Deferred Income Taxes - Net	(150)			(134)
Long-term lease liabilities	0
Other Long-term Liabilities	675			721
Total Liabilities	25,324			21,483
Shareholders' Equity
Common Stock, $1 Par Value	782			818
Other Capital	314			249
Retained Earnings	11,416			12,157
Accumulated Other Comprehensive Loss	(648)			(661)
Noncontrolling Interest	0			0
Total Shareholders' Equity	11,864			12,563
Total Liabilities and Shareholders' Equity	37,188			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	33,966			32,033
CSX Transportation
Current Assets:
Cash and Cash Equivalents	152			130	$ 116			$ 121
Short-term Investments	0			0
Accounts Receivable - Net	1,044			1,003
Receivable from Affiliates	6,918			5,214
Materials and Supplies	235			263
Other Current Assets	50			104
Total Current Assets	8,399			6,714
Properties	42,055			41,897
Accumulated Depreciation	(11,231)			(11,194)
Properties - Net	30,824			30,703
Right-of-Use Lease Asset	519
Other Long-term Assets	608			598
Total Assets	41,254			38,874
Current Liabilities:
Accounts Payable	832			763
Labor and Fringe Benefits Payable	411			440
Payable to Affiliates	385			633
Casualty, Environmental and Other Reserves	95			99
Current Maturities of Long-term Debt	245			18
Income and Other Taxes Payable	570			392
Other Current Liabilities	197			162
Total Current Liabilities	2,735			2,507
Casualty, Environmental and Other Reserves	161			176
Long-term Debt	460			710
Deferred Income Taxes - Net	6,755			6,601
Long-term lease liabilities	481
Other Long-term Liabilities	203			211
Total Liabilities	10,795			10,205
Shareholders' Equity
Common Stock, $1 Par Value	181			181
Other Capital	5,096			5,096
Retained Earnings	25,118			23,322
Accumulated Other Comprehensive Loss	49			53
Noncontrolling Interest	15			17
Total Shareholders' Equity	30,459			28,669
Total Liabilities and Shareholders' Equity	41,254			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	904			859
CSX Transportation | Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Other Companies	$ 0			$ 0