Summarized Consolidating Financial Data (Balance Sheets) (Details) - USD ($) $ in Millions	Dec. 30, 2016	Dec. 25, 2015	Dec. 26, 2014	Dec. 27, 2013
Current Assets:
Cash and Cash Equivalents	$ 603	$ 628	$ 669	$ 592
Short-term Investments	417	810
Accounts Receivable - Net	938	982
Receivable from Affiliates	0	0
Materials and Supplies	407	350
Other Current Assets	122	70
Total Current Assets	2,487	2,840
Properties	43,227	41,574
Accumulated Depreciation	(12,077)	(11,400)
Properties - Net	31,150	30,174
Other Long-term Assets	318	337
Total Assets	35,414	34,745
Current Liabilities:
Accounts Payable	806	764
Labor and Fringe Benefits Payable	545	490
Payable to Affiliates	0	0
Casualty, Environmental and Other Reserves	115	131
Current Maturities of Long-term Debt	331	20
Income and Other Taxes Payable	129	108
Other Current Liabilities	114	439
Total Current Liabilities	2,040	1,952
Casualty, Environmental and Other Reserves	259	269
Long-term Debt	10,962	10,515
Deferred Income Taxes - Net	9,596	9,179
Other Long-term Liabilities	863	1,162
Total Liabilities	23,720	23,077
Shareholders' Equity:
Common Stock, $1 Par Value	928	966
Other Capital	138	113
Retained Earnings	11,253	11,238
Accumulated Other Comprehensive Loss	(640)	(665)	(666)	(523)
Noncontrolling Minority Interest	15	16
Total Shareholders' Equity	11,694	11,668	11,176	10,504
Total Liabilities and Shareholders' Equity	35,414	34,745
Investments in Conrail
Current Assets:
Investment in Affiliates, Subsidiaries and Other	840	803
Affiliates and Other Companies
Current Assets:
Investment in Affiliates, Subsidiaries and Other	619	591
Investment in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates, Subsidiaries and Other	0	0
CSX Corporation
Current Assets:
Cash and Cash Equivalents	305	444	510	439
Short-term Investments	415	810
Accounts Receivable - Net	2	1
Receivable from Affiliates	1,157	1,092
Materials and Supplies	0	0
Other Current Assets	0	(59)
Total Current Assets	1,879	2,288
Properties	1	1
Accumulated Depreciation	(1)	(1)
Properties - Net	0	0
Other Long-term Assets	2	8
Total Assets	26,021	25,012
Current Liabilities:
Accounts Payable	95	108
Labor and Fringe Benefits Payable	40	36
Payable to Affiliates	3,457	2,954
Casualty, Environmental and Other Reserves	0	0
Current Maturities of Long-term Debt	313	1
Income and Other Taxes Payable	(346)	(87)
Other Current Liabilities	0	0
Total Current Liabilities	3,559	3,012
Casualty, Environmental and Other Reserves	0	0
Long-term Debt	10,203	9,732
Deferred Income Taxes - Net	(203)	(188)
Other Long-term Liabilities	783	804
Total Liabilities	14,342	13,360
Shareholders' Equity:
Common Stock, $1 Par Value	928	966
Other Capital	138	113
Retained Earnings	11,253	11,238
Accumulated Other Comprehensive Loss	(640)	(665)
Noncontrolling Minority Interest	0	0
Total Shareholders' Equity	11,679	11,652
Total Liabilities and Shareholders' Equity	26,021	25,012
CSX Corporation | Investments in Conrail
Current Assets:
Investment in Affiliates, Subsidiaries and Other	0	0
CSX Corporation | Affiliates and Other Companies
Current Assets:
Investment in Affiliates, Subsidiaries and Other	(39)	(39)
CSX Corporation | Investment in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates, Subsidiaries and Other	24,179	22,755
CSX Transportation
Current Assets:
Cash and Cash Equivalents	281	175	100	91
Short-term Investments	0	0
Accounts Receivable - Net	215	198
Receivable from Affiliates	2,351	2,038
Materials and Supplies	407	350
Other Current Assets	106	120
Total Current Assets	3,360	2,881
Properties	40,518	38,964
Accumulated Depreciation	(10,634)	(10,016)
Properties - Net	29,884	28,948
Other Long-term Assets	607	399
Total Assets	34,494	32,886
Current Liabilities:
Accounts Payable	678	626
Labor and Fringe Benefits Payable	440	407
Payable to Affiliates	500	437
Casualty, Environmental and Other Reserves	102	115
Current Maturities of Long-term Debt	19	19
Income and Other Taxes Payable	459	183
Other Current Liabilities	112	437
Total Current Liabilities	2,310	2,224
Casualty, Environmental and Other Reserves	208	219
Long-term Debt	759	783
Deferred Income Taxes - Net	9,541	9,141
Other Long-term Liabilities	410	484
Total Liabilities	13,228	12,851
Shareholders' Equity:
Common Stock, $1 Par Value	181	181
Other Capital	5,095	5,091
Retained Earnings	15,994	14,774
Accumulated Other Comprehensive Loss	(19)	(31)
Noncontrolling Minority Interest	15	20
Total Shareholders' Equity	21,266	20,035
Total Liabilities and Shareholders' Equity	34,494	32,886
CSX Transportation | Investments in Conrail
Current Assets:
Investment in Affiliates, Subsidiaries and Other	0	0
CSX Transportation | Affiliates and Other Companies
Current Assets:
Investment in Affiliates, Subsidiaries and Other	643	658
CSX Transportation | Investment in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates, Subsidiaries and Other	0	0
Eliminations and Other
Current Assets:
Cash and Cash Equivalents	17	9	$ 59	$ 62
Short-term Investments	2	0
Accounts Receivable - Net	721	783
Receivable from Affiliates	(3,508)	(3,130)
Materials and Supplies	0	0
Other Current Assets	16	9
Total Current Assets	(2,752)	(2,329)
Properties	2,708	2,609
Accumulated Depreciation	(1,442)	(1,383)
Properties - Net	1,266	1,226
Other Long-term Assets	(291)	(70)
Total Assets	(25,101)	(23,153)
Current Liabilities:
Accounts Payable	33	30
Labor and Fringe Benefits Payable	65	47
Payable to Affiliates	(3,957)	(3,391)
Casualty, Environmental and Other Reserves	13	16
Current Maturities of Long-term Debt	(1)	0
Income and Other Taxes Payable	16	12
Other Current Liabilities	2	2
Total Current Liabilities	(3,829)	(3,284)
Casualty, Environmental and Other Reserves	51	50
Long-term Debt	0	0
Deferred Income Taxes - Net	258	226
Other Long-term Liabilities	(330)	(126)
Total Liabilities	(3,850)	(3,134)
Shareholders' Equity:
Common Stock, $1 Par Value	(181)	(181)
Other Capital	(5,095)	(5,091)
Retained Earnings	(15,994)	(14,774)
Accumulated Other Comprehensive Loss	19	31
Noncontrolling Minority Interest	0	(4)
Total Shareholders' Equity	(21,251)	(20,019)
Total Liabilities and Shareholders' Equity	(25,101)	(23,153)
Eliminations and Other | Investments in Conrail
Current Assets:
Investment in Affiliates, Subsidiaries and Other	840	803
Eliminations and Other | Affiliates and Other Companies
Current Assets:
Investment in Affiliates, Subsidiaries and Other	15	(28)
Eliminations and Other | Investment in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates, Subsidiaries and Other	$ (24,179)	$ (22,755)