Summarized Consolidating Financial Data (Balance Sheets) (Details) - USD ($) $ in Millions	Dec. 25, 2015	Dec. 26, 2014	Dec. 27, 2013	Dec. 28, 2012
Current Assets:
Cash and Cash Equivalents	$ 628	$ 669	$ 592	$ 784
Short-term Investments	810	292
Accounts Receivable - Net	982	1,129
Receivable from Affiliates	0	0
Materials and Supplies	350	273
Deferred Income Taxes	126	141
Other Current Assets	70	68
Total Current Assets	2,966	2,572
Properties	41,574	39,343
Accumulated Depreciation	(11,400)	(10,759)
Properties - Net	30,174	28,584
Other Long-term Assets	505	541
Total Assets	35,039	33,053
Current Liabilities:
Accounts Payable	764	845
Labor and Fringe Benefits Payable	490	613
Payable to Affiliates	0	0
Casualty, Environmental and Other Reserves	131	142
Current Maturities of Long-term Debt	20	228
Income and Other Taxes Payable	108	163
Other Current Liabilities	439	116
Total Current Liabilities	1,952	2,107
Casualty, Environmental and Other Reserves	269	276
Long-term Debt	10,683	9,514
Deferred Income Taxes	9,305	8,858
Other Long-term Liabilities	1,162	1,122
Total Liabilities	23,371	21,877
Shareholders' Equity:
Common Stock, $1 Par Value	966	992
Other Capital	113	92
Retained Earnings	11,238	10,734
Accumulated Other Comprehensive Loss	(665)	(666)	(523)	(936)
Noncontrolling Minority Interest	16	24
Total Shareholders' Equity	11,668	11,176	10,504	9,136
Total Liabilities and Shareholders' Equity	35,039	33,053
Investments in Conrail
Current Assets:
Investment in Affiliates, Subsidiaries and Other	803	779
Affiliates and Other Companies
Current Assets:
Investment in Affiliates, Subsidiaries and Other	591	577
Investment in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates, Subsidiaries and Other	0	0
CSX Corporation
Current Assets:
Cash and Cash Equivalents	444	510	439	481
Short-term Investments	810	250
Accounts Receivable - Net	1	2
Receivable from Affiliates	1,092	1,211
Materials and Supplies	0	0
Deferred Income Taxes	10	3
Other Current Assets	(59)	0
Total Current Assets	2,298	1,976
Properties	1	1
Accumulated Depreciation	(1)	(1)
Properties - Net	0	0
Other Long-term Assets	176	178
Total Assets	25,190	23,685
Current Liabilities:
Accounts Payable	108	106
Labor and Fringe Benefits Payable	36	38
Payable to Affiliates	2,954	3,053
Casualty, Environmental and Other Reserves	0	0
Current Maturities of Long-term Debt	1	200
Income and Other Taxes Payable	(87)	(150)
Other Current Liabilities	0	0
Total Current Liabilities	3,012	3,247
Casualty, Environmental and Other Reserves	0	0
Long-term Debt	9,900	8,705
Deferred Income Taxes	(178)	(172)
Other Long-term Liabilities	804	753
Total Liabilities	13,538	12,533
Shareholders' Equity:
Common Stock, $1 Par Value	966	992
Other Capital	113	92
Retained Earnings	11,238	10,734
Accumulated Other Comprehensive Loss	(665)	(666)
Noncontrolling Minority Interest	0	0
Total Shareholders' Equity	11,652	11,152
Total Liabilities and Shareholders' Equity	25,190	23,685
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	22,755	21,570
CSX Transportation
Current Assets:
Cash and Cash Equivalents	175	100	91	235
Short-term Investments	0	0
Accounts Receivable - Net	198	206
Receivable from Affiliates	2,038	2,418
Materials and Supplies	350	272
Deferred Income Taxes	117	139
Other Current Assets	120	61
Total Current Assets	2,998	3,196
Properties	38,964	36,888
Accumulated Depreciation	(10,016)	(9,516)
Properties - Net	28,948	27,372
Other Long-term Assets	399	387
Total Assets	33,003	31,599
Current Liabilities:
Accounts Payable	626	707
Labor and Fringe Benefits Payable	407	511
Payable to Affiliates	437	514
Casualty, Environmental and Other Reserves	115	126
Current Maturities of Long-term Debt	19	29
Income and Other Taxes Payable	183	293
Other Current Liabilities	437	111
Total Current Liabilities	2,224	2,291
Casualty, Environmental and Other Reserves	219	213
Long-term Debt	783	809
Deferred Income Taxes	9,258	8,827
Other Long-term Liabilities	484	487
Total Liabilities	12,968	12,627
Shareholders' Equity:
Common Stock, $1 Par Value	181	181
Other Capital	5,091	5,077
Retained Earnings	14,774	13,717
Accumulated Other Comprehensive Loss	(31)	(31)
Noncontrolling Minority Interest	20	28
Total Shareholders' Equity	20,035	18,972
Total Liabilities and Shareholders' Equity	33,003	31,599
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	658	644
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	9	59	$ 62	$ 68
Short-term Investments	0	42
Accounts Receivable - Net	783	921
Receivable from Affiliates	(3,130)	(3,629)
Materials and Supplies	0	1
Deferred Income Taxes	(1)	(1)
Other Current Assets	9	7
Total Current Assets	(2,330)	(2,600)
Properties	2,609	2,454
Accumulated Depreciation	(1,383)	(1,242)
Properties - Net	1,226	1,212
Other Long-term Assets	(70)	(24)
Total Assets	(23,154)	(22,231)
Current Liabilities:
Accounts Payable	30	32
Labor and Fringe Benefits Payable	47	64
Payable to Affiliates	(3,391)	(3,567)
Casualty, Environmental and Other Reserves	16	16
Current Maturities of Long-term Debt	0	(1)
Income and Other Taxes Payable	12	20
Other Current Liabilities	2	5
Total Current Liabilities	(3,284)	(3,431)
Casualty, Environmental and Other Reserves	50	63
Long-term Debt	0	0
Deferred Income Taxes	225	203
Other Long-term Liabilities	(126)	(118)
Total Liabilities	(3,135)	(3,283)
Shareholders' Equity:
Common Stock, $1 Par Value	(181)	(181)
Other Capital	(5,091)	(5,077)
Retained Earnings	(14,774)	(13,717)
Accumulated Other Comprehensive Loss	31	31
Noncontrolling Minority Interest	(4)	(4)
Total Shareholders' Equity	(20,019)	(18,948)
Total Liabilities and Shareholders' Equity	(23,154)	(22,231)
Eliminations and Other | Investments in Conrail
Current Assets:
Investment in Affiliates, Subsidiaries and Other	803	779
Eliminations and Other | Affiliates and Other Companies
Current Assets:
Investment in Affiliates, Subsidiaries and Other	(28)	(28)
Eliminations and Other | Investment in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates, Subsidiaries and Other	$ (22,755)	$ (21,570)