Summarized Consolidating Financial Data - Consolidating Balance Sheet (Details) - USD ($) $ / shares in Units, $ in Millions	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Current Assets:
Cash and Cash Equivalents	$ 853		$ 858	$ 1,320		$ 401
Short-term Investments	878		253
Accounts Receivable - Net	1,111		1,010
Receivable from Affiliates	0		0
Materials and Supplies	222		263
Other Current Assets	122		181
Total Current Assets	3,186		2,565
Properties	44,756		44,805
Accumulated Depreciation	(12,737)		(12,807)
Properties - Net	32,019		31,998
Right-of-Use Lease Asset	550		0
Other Long-term Assets	347		387
Total Assets	37,924		36,729
Current Liabilities:
Accounts Payable	989		949
Labor and Fringe Benefits Payable	412		550
Payable to Affiliates	0		0
Casualty, Environmental and Other Reserves	110		113
Current Maturities of Long-term Debt	245		18
Income and Other Taxes Payable	133		106
Other Current Liabilities	164		179
Total Current Liabilities	2,053		1,915
Casualty, Environmental and Other Reserves	199		211
Long-term Debt	15,522		14,739
Deferred Income Taxes - Net	6,791		6,690
Long-term lease liabilities	501		0
Other Long-term Liabilities	568		594
Total Liabilities	25,634		24,149
Shareholders' Equity
Common Stock, $1 Par Value	798		818
Other Capital	290		249
Retained Earnings	11,843		12,157
Accumulated Other Comprehensive Loss	(655)		(661)
Noncontrolling Interest	14		17
Total Shareholders' Equity	12,290	$ 12,445	12,580	14,023	$ 14,391	14,721
Total Liabilities and Shareholders' Equity	$ 37,924		$ 36,729
Common stock, par value (in dollars per share)	$ 1		$ 1
Investments in Conrail
Current Assets:
Investment in Affiliates and Other Companies	$ 959		$ 943
Affiliates and Other Companies
Current Assets:
Investment in Affiliates and Other Companies	863		836
Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Other Companies	0		0
Eliminations and Other
Current Assets:
Cash and Cash Equivalents	11		12	5		6
Short-term Investments	9		3
Accounts Receivable - Net	51		6
Receivable from Affiliates	(7,087)		(6,234)
Materials and Supplies	0		0
Other Current Assets	21		14
Total Current Assets	(6,995)		(6,199)
Properties	2,934		2,907
Accumulated Depreciation	(1,662)		(1,612)
Properties - Net	1,272		1,295
Right-of-Use Lease Asset	21
Other Long-term Assets	(247)		(213)
Total Assets	(38,306)		(36,191)
Current Liabilities:
Accounts Payable	53		54
Labor and Fringe Benefits Payable	35		69
Payable to Affiliates	(8,565)		(7,606)
Casualty, Environmental and Other Reserves	15		14
Current Maturities of Long-term Debt	0		0
Income and Other Taxes Payable	37		4
Other Current Liabilities	11		6
Total Current Liabilities	(8,414)		(7,459)
Casualty, Environmental and Other Reserves	35		35
Long-term Debt	0		0
Deferred Income Taxes - Net	222		223
Long-term lease liabilities	15
Other Long-term Liabilities	(334)		(338)
Total Liabilities	(8,476)		(7,539)
Shareholders' Equity
Common Stock, $1 Par Value	(181)		(181)
Other Capital	(5,096)		(5,096)
Retained Earnings	(24,503)		(23,322)
Accumulated Other Comprehensive Loss	(50)		(53)
Noncontrolling Interest	0		0
Total Shareholders' Equity	(29,830)		(28,652)
Total Liabilities and Shareholders' Equity	(38,306)		(36,191)
Eliminations and Other | Investments in Conrail
Current Assets:
Investment in Affiliates and Other Companies	959		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	(33,332)		(32,033)
CSX Corporation
Current Assets:
Cash and Cash Equivalents	718		716	1,172		274
CSX Corporation | Corporate, Non-Segment
Current Assets:
Cash and Cash Equivalents	718		716
Short-term Investments	869		250
Accounts Receivable - Net	2		1
Receivable from Affiliates	921		1,020
Materials and Supplies	0		0
Other Current Assets	3		63
Total Current Assets	2,513		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	35,809		34,046
Current Liabilities:
Accounts Payable	153		132
Labor and Fringe Benefits Payable	35		41
Payable to Affiliates	8,154		6,973
Casualty, Environmental and Other Reserves	0		0
Current Maturities of Long-term Debt	0		0
Income and Other Taxes Payable	(423)		(290)
Other Current Liabilities	0		11
Total Current Liabilities	7,919		6,867
Casualty, Environmental and Other Reserves	0		0
Long-term Debt	15,042		14,029
Deferred Income Taxes - Net	(121)		(134)
Long-term lease liabilities	0
Other Long-term Liabilities	693		721
Total Liabilities	23,533		21,483
Shareholders' Equity
Common Stock, $1 Par Value	798		818
Other Capital	290		249
Retained Earnings	11,843		12,157
Accumulated Other Comprehensive Loss	(655)		(661)
Noncontrolling Interest	0		0
Total Shareholders' Equity	12,276		12,563
Total Liabilities and Shareholders' Equity	35,809		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	33,332		32,033
CSX Transportation
Current Assets:
Cash and Cash Equivalents	124		130	$ 143		$ 121
Short-term Investments	0		0
Accounts Receivable - Net	1,058		1,003
Receivable from Affiliates	6,166		5,214
Materials and Supplies	222		263
Other Current Assets	98		104
Total Current Assets	7,668		6,714
Properties	41,821		41,897
Accumulated Depreciation	(11,074)		(11,194)
Properties - Net	30,747		30,703
Right-of-Use Lease Asset	529
Other Long-term Assets	591		598
Total Assets	40,421		38,874
Current Liabilities:
Accounts Payable	783		763
Labor and Fringe Benefits Payable	342		440
Payable to Affiliates	411		633
Casualty, Environmental and Other Reserves	95		99
Current Maturities of Long-term Debt	245		18
Income and Other Taxes Payable	519		392
Other Current Liabilities	153		162
Total Current Liabilities	2,548		2,507
Casualty, Environmental and Other Reserves	164		176
Long-term Debt	480		710
Deferred Income Taxes - Net	6,690		6,601
Long-term lease liabilities	486
Other Long-term Liabilities	209		211
Total Liabilities	10,577		10,205
Shareholders' Equity
Common Stock, $1 Par Value	181		181
Other Capital	5,096		5,096
Retained Earnings	24,503		23,322
Accumulated Other Comprehensive Loss	50		53
Noncontrolling Interest	14		17
Total Shareholders' Equity	29,844		28,669
Total Liabilities and Shareholders' Equity	40,421		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	886		859
CSX Transportation | Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Other Companies	$ 0		$ 0