Summarized Consolidating Financial Data (Balance Sheets) (Details) (USD $) In Millions, unless otherwise specified	Dec. 26, 2014	Dec. 27, 2013	Dec. 28, 2012	Dec. 30, 2011
Current Assets:
Cash and Cash Equivalents	$ 669	$ 592	$ 784	$ 783
Short-term Investments	292	487
Accounts Receivable - Net	1,129	1,052
Receivable from Affiliates	0	0
Materials and Supplies	273	252
Deferred Income Taxes	141	155
Other Current Assets	68	64
Total Current Assets	2,572	2,602
Properties	39,343	37,184
Accumulated Depreciation	(10,759)	(9,893)
Properties - Net	28,584	27,291
Other Long-term Assets	541	591
Total Assets	33,053	31,782
Current Liabilities:
Accounts Payable	845	957
Labor and Fringe Benefits Payable	613	587
CSX Payable to Conrail	0	0
Casualty, Environmental and Other Reserves	142	151
Current Maturities of Long-term Debt	228	533
Income and Other Taxes Payable	163	91
Other Current Liabilities	116	105
Total Current Liabilities	2,107	2,424
Loss Contingency, Accrual, Noncurrent	276	300
Long-term Debt	9,514	9,022
Deferred Income Taxes	8,858	8,662
Other Long-term Liabilities	1,122	870
Total Liabilities	21,877	21,278
Shareholders' Equity:
Common Stock, $1 Par Value	992	1,009
Other Capital	92	61
Retained Earnings	10,734	9,936
Accumulated Other Comprehensive Loss	(666)	(523)	(936)	(875)
Noncontrolling Minority Interest	24	21
Total Shareholders' Equity	11,176	10,504	9,136	8,598
Total Liabilities and Shareholders' Equity	33,053	31,782
Investments in Conrail
Current Assets:
Investment in Affiliates, Subsidiaries, and Joint Ventures	779	752
Affiliates and Other Companies
Current Assets:
Investment in Affiliates, Subsidiaries, and Joint Ventures	577	546
Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates, Subsidiaries, and Joint Ventures	0	0
CSX Corporation
Current Assets:
Cash and Cash Equivalents	510	439	481	549
Short-term Investments	250	472
Accounts Receivable - Net	2	3
Receivable from Affiliates	1,211	1,141
Materials and Supplies	0	0
Deferred Income Taxes	3	(5)
Other Current Assets	0	1
Total Current Assets	1,976	2,051
Properties	1	1
Accumulated Depreciation	(1)	(1)
Properties - Net	0	0
Other Long-term Assets	178	217
Total Assets	23,685	22,455
Current Liabilities:
Accounts Payable	106	110
Labor and Fringe Benefits Payable	38	38
CSX Payable to Conrail	3,053	3,298
Casualty, Environmental and Other Reserves	0	0
Current Maturities of Long-term Debt	200	200
Income and Other Taxes Payable	(150)	(397)
Other Current Liabilities	0	0
Total Current Liabilities	3,247	3,249
Loss Contingency, Accrual, Noncurrent	0	0
Long-term Debt	8,705	8,308
Deferred Income Taxes	(172)	(64)
Other Long-term Liabilities	753	479
Total Liabilities	12,533	11,972
Shareholders' Equity:
Common Stock, $1 Par Value	992	1,009
Other Capital	92	61
Retained Earnings	10,734	9,936
Accumulated Other Comprehensive Loss	(666)	(523)
Noncontrolling Minority Interest	0	0
Total Shareholders' Equity	11,152	10,483
Total Liabilities and Shareholders' Equity	23,685	22,455
CSX Corporation | Investments in Conrail
Current Assets:
Investment in Affiliates, Subsidiaries, and Joint Ventures	0	0
CSX Corporation | Affiliates and Other Companies
Current Assets:
Investment in Affiliates, Subsidiaries, and Joint Ventures	(39)	(39)
CSX Corporation | Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates, Subsidiaries, and Joint Ventures	21,570	20,226
CSX Transportation
Current Assets:
Cash and Cash Equivalents	100	91	235	154
Short-term Investments	0	0
Accounts Receivable - Net	206	240
Receivable from Affiliates	2,418	2,635
Materials and Supplies	272	252
Deferred Income Taxes	139	161
Other Current Assets	61	57
Total Current Assets	3,196	3,436
Properties	36,888	34,987
Accumulated Depreciation	(9,516)	(8,778)
Properties - Net	27,372	26,209
Other Long-term Assets	387	388
Total Assets	31,599	30,645
Current Liabilities:
Accounts Payable	707	809
Labor and Fringe Benefits Payable	511	491
CSX Payable to Conrail	514	535
Casualty, Environmental and Other Reserves	126	136
Current Maturities of Long-term Debt	29	333
Income and Other Taxes Payable	293	479
Other Current Liabilities	111	103
Total Current Liabilities	2,291	2,886
Loss Contingency, Accrual, Noncurrent	213	231
Long-term Debt	809	714
Deferred Income Taxes	8,827	8,548
Other Long-term Liabilities	487	512
Total Liabilities	12,627	12,891
Shareholders' Equity:
Common Stock, $1 Par Value	181	181
Other Capital	5,077	5,077
Retained Earnings	13,717	12,514
Accumulated Other Comprehensive Loss	(31)	(43)
Noncontrolling Minority Interest	28	25
Total Shareholders' Equity	18,972	17,754
Total Liabilities and Shareholders' Equity	31,599	30,645
CSX Transportation | Investments in Conrail
Current Assets:
Investment in Affiliates, Subsidiaries, and Joint Ventures	0	0
CSX Transportation | Affiliates and Other Companies
Current Assets:
Investment in Affiliates, Subsidiaries, and Joint Ventures	644	612
CSX Transportation | Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates, Subsidiaries, and Joint Ventures	0	0
Eliminations and Other
Current Assets:
Cash and Cash Equivalents	59	62	68	80
Short-term Investments	42	15
Accounts Receivable - Net	921	809
Receivable from Affiliates	(3,629)	(3,776)
Materials and Supplies	1	0
Deferred Income Taxes	(1)	(1)
Other Current Assets	7	6
Total Current Assets	(2,600)	(2,885)
Properties	2,454	2,196
Accumulated Depreciation	(1,242)	(1,114)
Properties - Net	1,212	1,082
Other Long-term Assets	(24)	(14)
Total Assets	(22,231)	(21,318)
Current Liabilities:
Accounts Payable	32	38
Labor and Fringe Benefits Payable	64	58
CSX Payable to Conrail	(3,567)	(3,833)
Casualty, Environmental and Other Reserves	16	15
Current Maturities of Long-term Debt	(1)	0
Income and Other Taxes Payable	20	9
Other Current Liabilities	5	2
Total Current Liabilities	(3,431)	(3,711)
Loss Contingency, Accrual, Noncurrent	63	69
Long-term Debt	0	0
Deferred Income Taxes	203	178
Other Long-term Liabilities	(118)	(121)
Total Liabilities	(3,283)	(3,585)
Shareholders' Equity:
Common Stock, $1 Par Value	(181)	(181)
Other Capital	(5,077)	(5,077)
Retained Earnings	(13,717)	(12,514)
Accumulated Other Comprehensive Loss	31	43
Noncontrolling Minority Interest	(4)	(4)
Total Shareholders' Equity	(18,948)	(17,733)
Total Liabilities and Shareholders' Equity	(22,231)	(21,318)
Eliminations and Other | Investments in Conrail
Current Assets:
Investment in Affiliates, Subsidiaries, and Joint Ventures	779	752
Eliminations and Other | Affiliates and Other Companies
Current Assets:
Investment in Affiliates, Subsidiaries, and Joint Ventures	(28)	(27)
Eliminations and Other | Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates, Subsidiaries, and Joint Ventures	$ (21,570)	$ (20,226)