Summarized Consolidating Financial Data - Consolidating Balance Sheet (Details) (USD $) In Millions, unless otherwise specified	Mar. 27, 2015	Dec. 26, 2014	Mar. 28, 2014	Dec. 27, 2013
Current Assets:
Cash and Cash Equivalents	$ 561	$ 669	$ 475	$ 592
Short-term Investments	257	292
Accounts Receivable - Net	1,103	1,129
Receivable from Affiliates	0	0
Materials and Supplies	291	273
Deferred Income Taxes	146	141
Other Current Assets	99	68
Total Current Assets	2,457	2,572
Properties	39,824	39,343
Accumulated Depreciation	(10,952)	(10,759)
Properties - Net	28,872	28,584
Other Long-term Assets	479	541
Total Assets	33,161	33,053
Current Liabilities:
Accounts Payable	858	845
Labor and Fringe Benefits Payable	410	613
Payable to Affiliates	0	0
Casualty, Environmental and Other Reserves	141	142
Current Maturities of Long-term Debt	228	228
Income and Other Taxes Payable	288	163
Other Current Liabilities	113	116
Total Current Liabilities	2,038	2,107
Casualty, Environmental and Other Reserves	286	276
Long-term Debt	9,513	9,514
Deferred Income Taxes	8,886	8,858
Other Long-term Liabilities	1,100	1,122
Total Liabilities	21,823	21,877
Shareholders' Equity
Common Stock $1 Par Value	988	992
Other Capital	100	92
Retained Earnings	10,895	10,734
Accumulated Other Comprehensive Loss	(668)	(666)
Noncontrolling Interest	23	24
Total Shareholders' Equity	11,338	11,176
Total Liabilities and Shareholders' Equity	33,161	33,053
Investments in Conrail
Current Assets:
Investment in Affiliates and Consolidated Subsidiaries	778	779
Affiliates and Other Companies
Current Assets:
Investment in Affiliates and Consolidated Subsidiaries	575	577
Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Consolidated Subsidiaries	0	0
CSX Corporation
Current Assets:
Cash and Cash Equivalents	363	510	321	439
Short-term Investments	250	250
Accounts Receivable - Net	2	2
Receivable from Affiliates	1,324	1,211
Materials and Supplies	0	0
Deferred Income Taxes	0	3
Other Current Assets	4	0
Total Current Assets	1,943	1,976
Properties	1	1
Accumulated Depreciation	(1)	(1)
Properties - Net	0	0
Other Long-term Assets	169	178
Total Assets	23,861	23,685
Current Liabilities:
Accounts Payable	167	106
Labor and Fringe Benefits Payable	34	38
Payable to Affiliates	3,035	3,053
Casualty, Environmental and Other Reserves	0	0
Current Maturities of Long-term Debt	200	200
Income and Other Taxes Payable	(183)	(150)
Other Current Liabilities	0	0
Total Current Liabilities	3,253	3,247
Casualty, Environmental and Other Reserves	0	0
Long-term Debt	8,706	8,705
Deferred Income Taxes	(167)	(172)
Other Long-term Liabilities	754	753
Total Liabilities	12,546	12,533
Shareholders' Equity
Common Stock $1 Par Value	988	992
Other Capital	100	92
Retained Earnings	10,895	10,734
Accumulated Other Comprehensive Loss	(668)	(666)
Noncontrolling Interest	0	0
Total Shareholders' Equity	11,315	11,152
Total Liabilities and Shareholders' Equity	23,861	23,685
CSX Corporation | Investments in Conrail
Current Assets:
Investment in Affiliates and Consolidated Subsidiaries	0	0
CSX Corporation | Affiliates and Other Companies
Current Assets:
Investment in Affiliates and Consolidated Subsidiaries	(39)	(39)
CSX Corporation | Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Consolidated Subsidiaries	21,788	21,570
CSX Transportation
Current Assets:
Cash and Cash Equivalents	142	100	91	91
Short-term Investments	0	0
Accounts Receivable - Net	124	206
Receivable from Affiliates	2,318	2,418
Materials and Supplies	290	272
Deferred Income Taxes	146	139
Other Current Assets	87	61
Total Current Assets	3,107	3,196
Properties	37,347	36,888
Accumulated Depreciation	(9,674)	(9,516)
Properties - Net	27,673	27,372
Other Long-term Assets	387	387
Total Assets	31,808	31,599
Current Liabilities:
Accounts Payable	662	707
Labor and Fringe Benefits Payable	346	511
Payable to Affiliates	539	514
Casualty, Environmental and Other Reserves	126	126
Current Maturities of Long-term Debt	29	29
Income and Other Taxes Payable	459	293
Other Current Liabilities	107	111
Total Current Liabilities	2,268	2,291
Casualty, Environmental and Other Reserves	224	213
Long-term Debt	807	809
Deferred Income Taxes	8,847	8,827
Other Long-term Liabilities	465	487
Total Liabilities	12,611	12,627
Shareholders' Equity
Common Stock $1 Par Value	181	181
Other Capital	5,078	5,077
Retained Earnings	13,945	13,717
Accumulated Other Comprehensive Loss	(34)	(31)
Noncontrolling Interest	27	28
Total Shareholders' Equity	19,197	18,972
Total Liabilities and Shareholders' Equity	31,808	31,599
CSX Transportation | Investments in Conrail
Current Assets:
Investment in Affiliates and Consolidated Subsidiaries	0	0
CSX Transportation | Affiliates and Other Companies
Current Assets:
Investment in Affiliates and Consolidated Subsidiaries	641	644
CSX Transportation | Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Consolidated Subsidiaries	0	0
Eliminations and Other
Current Assets:
Cash and Cash Equivalents	56	59	63	62
Short-term Investments	7	42
Accounts Receivable - Net	977	921
Receivable from Affiliates	(3,642)	(3,629)
Materials and Supplies	1	1
Deferred Income Taxes	0	(1)
Other Current Assets	8	7
Total Current Assets	(2,593)	(2,600)
Properties	2,476	2,454
Accumulated Depreciation	(1,277)	(1,242)
Properties - Net	1,199	1,212
Other Long-term Assets	(77)	(24)
Total Assets	(22,508)	(22,231)
Current Liabilities:
Accounts Payable	29	32
Labor and Fringe Benefits Payable	30	64
Payable to Affiliates	(3,574)	(3,567)
Casualty, Environmental and Other Reserves	15	16
Current Maturities of Long-term Debt	(1)	(1)
Income and Other Taxes Payable	12	20
Other Current Liabilities	6	5
Total Current Liabilities	(3,483)	(3,431)
Casualty, Environmental and Other Reserves	62	63
Long-term Debt	0	0
Deferred Income Taxes	206	203
Other Long-term Liabilities	(119)	(118)
Total Liabilities	(3,334)	(3,283)
Shareholders' Equity
Common Stock $1 Par Value	(181)	(181)
Other Capital	(5,078)	(5,077)
Retained Earnings	(13,945)	(13,717)
Accumulated Other Comprehensive Loss	34	31
Noncontrolling Interest	(4)	(4)
Total Shareholders' Equity	(19,174)	(18,948)
Total Liabilities and Shareholders' Equity	(22,508)	(22,231)
Eliminations and Other | Investments in Conrail
Current Assets:
Investment in Affiliates and Consolidated Subsidiaries	778	779
Eliminations and Other | Affiliates and Other Companies
Current Assets:
Investment in Affiliates and Consolidated Subsidiaries	(27)	(28)
Eliminations and Other | Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Consolidated Subsidiaries	$ (21,788)	$ (21,570)