Summarized Consolidating Financial Data - Consolidating Balance Sheet (Details) - USD ($) $ / shares in Units, $ in Millions	Mar. 25, 2016	Dec. 25, 2015	Mar. 27, 2015	Dec. 26, 2014
Current Assets:
Cash and Cash Equivalents	$ 731	$ 628	$ 561	$ 669
Short-term Investments	375	810
Accounts Receivable - Net	917	982
Receivable from Affiliates	0	0
Materials and Supplies	370	350
Deferred Income Taxes	132	126
Other Current Assets	83	70
Total Current Assets	2,608	2,966
Properties	41,865	41,574
Accumulated Depreciation	(11,572)	(11,400)
Properties - Net	30,293	30,174
Other Long-term Assets	307	337
Total Assets	34,610	34,871
Current Liabilities:
Accounts Payable	815	764
Labor and Fringe Benefits Payable	398	490
Payable to Affiliates	0	0
Casualty, Environmental and Other Reserves	130	131
Current Maturities of Long-term Debt	20	20
Income and Other Taxes Payable	170	108
Other Current Liabilities	159	439
Total Current Liabilities	1,692	1,952
Casualty, Environmental and Other Reserves	255	269
Long-term Debt	10,516	10,515
Deferred Income Taxes	9,396	9,305
Other Long-term Liabilities	1,145	1,162
Total Liabilities	23,004	23,203
Shareholders' Equity
Common Stock, $1 Par Value	956	966
Other Capital	112	113
Retained Earnings	11,183	11,238
Accumulated Other Comprehensive Loss	(658)	(665)
Noncontrolling Interest	13	16
Total Shareholders' Equity	11,606	11,668
Total Liabilities and Shareholders' Equity	$ 34,610	$ 34,871
Common stock, par value (in dollars per share)	$ 1	$ 1
Investments in Conrail
Current Assets:
Investment in Affiliates and Consolidated Subsidiaries	$ 811	$ 803
Affiliates and Other Companies
Current Assets:
Investment in Affiliates and Consolidated Subsidiaries	591	591
Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Consolidated Subsidiaries	0	0
CSX Corporation
Current Assets:
Cash and Cash Equivalents	493	444	363	510
Short-term Investments	375	810
Accounts Receivable - Net	0	1
Receivable from Affiliates	1,195	1,092
Materials and Supplies	0	0
Deferred Income Taxes	15	10
Other Current Assets	4	(59)
Total Current Assets	2,082	2,298
Properties	1	1
Accumulated Depreciation	(1)	(1)
Properties - Net	0	0
Other Long-term Assets	7	8
Total Assets	25,028	25,022
Current Liabilities:
Accounts Payable	168	108
Labor and Fringe Benefits Payable	33	36
Payable to Affiliates	3,045	2,954
Casualty, Environmental and Other Reserves	0	0
Current Maturities of Long-term Debt	1	1
Income and Other Taxes Payable	(174)	(87)
Other Current Liabilities	0	0
Total Current Liabilities	3,073	3,012
Casualty, Environmental and Other Reserves	0	0
Long-term Debt	9,734	9,732
Deferred Income Taxes	(172)	(178)
Other Long-term Liabilities	800	804
Total Liabilities	13,435	13,370
Shareholders' Equity
Common Stock, $1 Par Value	956	966
Other Capital	112	113
Retained Earnings	11,183	11,238
Accumulated Other Comprehensive Loss	(658)	(665)
Noncontrolling Interest	0	0
Total Shareholders' Equity	11,593	11,652
Total Liabilities and Shareholders' Equity	25,028	25,022
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	22,978	22,755
CSX Transportation
Current Assets:
Cash and Cash Equivalents	223	175	142	100
Short-term Investments	0	0
Accounts Receivable - Net	159	198
Receivable from Affiliates	2,000	2,038
Materials and Supplies	370	350
Deferred Income Taxes	118	117
Other Current Assets	72	120
Total Current Assets	2,942	2,998
Properties	39,220	38,964
Accumulated Depreciation	(10,151)	(10,016)
Properties - Net	29,069	28,948
Other Long-term Assets	399	399
Total Assets	33,024	33,003
Current Liabilities:
Accounts Payable	617	626
Labor and Fringe Benefits Payable	336	407
Payable to Affiliates	467	437
Casualty, Environmental and Other Reserves	114	115
Current Maturities of Long-term Debt	19	19
Income and Other Taxes Payable	303	183
Other Current Liabilities	156	437
Total Current Liabilities	2,012	2,224
Casualty, Environmental and Other Reserves	206	219
Long-term Debt	782	783
Deferred Income Taxes	9,338	9,258
Other Long-term Liabilities	472	484
Total Liabilities	12,810	12,968
Shareholders' Equity
Common Stock, $1 Par Value	181	181
Other Capital	5,091	5,091
Retained Earnings	14,956	14,774
Accumulated Other Comprehensive Loss	(31)	(31)
Noncontrolling Interest	17	20
Total Shareholders' Equity	20,214	20,035
Total Liabilities and Shareholders' Equity	33,024	33,003
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	614	658
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	15	9	$ 56	$ 59
Short-term Investments	0	0
Accounts Receivable - Net	758	783
Receivable from Affiliates	(3,195)	(3,130)
Materials and Supplies	0	0
Deferred Income Taxes	(1)	(1)
Other Current Assets	7	9
Total Current Assets	(2,416)	(2,330)
Properties	2,644	2,609
Accumulated Depreciation	(1,420)	(1,383)
Properties - Net	1,224	1,226
Other Long-term Assets	(99)	(70)
Total Assets	(23,442)	(23,154)
Current Liabilities:
Accounts Payable	30	30
Labor and Fringe Benefits Payable	29	47
Payable to Affiliates	(3,512)	(3,391)
Casualty, Environmental and Other Reserves	16	16
Current Maturities of Long-term Debt	0	0
Income and Other Taxes Payable	41	12
Other Current Liabilities	3	2
Total Current Liabilities	(3,393)	(3,284)
Casualty, Environmental and Other Reserves	49	50
Long-term Debt	0	0
Deferred Income Taxes	230	225
Other Long-term Liabilities	(127)	(126)
Total Liabilities	(3,241)	(3,135)
Shareholders' Equity
Common Stock, $1 Par Value	(181)	(181)
Other Capital	(5,091)	(5,091)
Retained Earnings	(14,956)	(14,774)
Accumulated Other Comprehensive Loss	31	31
Noncontrolling Interest	(4)	(4)
Total Shareholders' Equity	(20,201)	(20,019)
Total Liabilities and Shareholders' Equity	(23,442)	(23,154)
Eliminations and Other | Investments in Conrail
Current Assets:
Investment in Affiliates and Consolidated Subsidiaries	811	803
Eliminations and Other | Affiliates and Other Companies
Current Assets:
Investment in Affiliates and Consolidated Subsidiaries	16	(28)
Eliminations and Other | Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Consolidated Subsidiaries	$ (22,978)	$ (22,755)