Summarized Consolidating Financial Data - Consolidating Balance Sheet (Details) - USD ($) $ / shares in Units, $ in Millions	Jun. 24, 2016	Dec. 25, 2015	Jun. 26, 2015	Dec. 26, 2014
Current Assets:
Cash and Cash Equivalents	$ 566	$ 628	$ 438	$ 669
Short-term Investments	262	810
Accounts Receivable - Net	912	982
Receivable from Affiliates	0	0
Materials and Supplies	399	350
Other Current Assets	89	70
Total Current Assets	2,228	2,840
Properties	42,345	41,574
Accumulated Depreciation	(11,738)	(11,400)
Properties - Net	30,607	30,174
Other Long-term Assets	302	337
Total Assets	34,550	34,745
Current Liabilities:
Accounts Payable	766	764
Labor and Fringe Benefits Payable	464	490
Payable to Affiliates	0	0
Casualty, Environmental and Other Reserves	133	131
Current Maturities of Long-term Debt	632	20
Income and Other Taxes Payable	137	108
Other Current Liabilities	150	439
Total Current Liabilities	2,282	1,952
Casualty, Environmental and Other Reserves	246	269
Long-term Debt	9,905	10,515
Deferred Income Taxes - Net	9,355	9,179
Other Long-term Liabilities	1,137	1,162
Total Liabilities	22,925	23,077
Shareholders' Equity
Common Stock, $1 Par Value	946	966
Other Capital	116	113
Retained Earnings	11,199	11,238
Accumulated Other Comprehensive Loss	(649)	(665)
Noncontrolling Interest	13	16
Total Shareholders' Equity	11,625	11,668
Total Liabilities and Shareholders' Equity	$ 34,550	$ 34,745
Common stock, par value (in dollars per share)	$ 1	$ 1
Investments in Conrail
Current Assets:
Investment in Affiliates and Consolidated Subsidiaries	$ 818	$ 803
Affiliates and Other Companies
Current Assets:
Investment in Affiliates and Consolidated Subsidiaries	595	591
Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Consolidated Subsidiaries	0	0
CSX Corporation
Current Assets:
Cash and Cash Equivalents	420	444	233	510
Short-term Investments	260	810
Accounts Receivable - Net	(1)	1
Receivable from Affiliates	1,088	1,092
Materials and Supplies	0	0
Other Current Assets	7	(59)
Total Current Assets	1,774	2,288
Properties	1	1
Accumulated Depreciation	(1)	(1)
Properties - Net	0	0
Other Long-term Assets	3	8
Total Assets	25,060	25,012
Current Liabilities:
Accounts Payable	108	108
Labor and Fringe Benefits Payable	36	36
Payable to Affiliates	3,304	2,954
Casualty, Environmental and Other Reserves	0	0
Current Maturities of Long-term Debt	613	1
Income and Other Taxes Payable	(334)	(87)
Other Current Liabilities	0	0
Total Current Liabilities	3,727	3,012
Casualty, Environmental and Other Reserves	0	0
Long-term Debt	9,125	9,732
Deferred Income Taxes - Net	(197)	(188)
Other Long-term Liabilities	793	804
Total Liabilities	13,448	13,360
Shareholders' Equity
Common Stock, $1 Par Value	946	966
Other Capital	116	113
Retained Earnings	11,199	11,238
Accumulated Other Comprehensive Loss	(649)	(665)
Noncontrolling Interest	0	0
Total Shareholders' Equity	11,612	11,652
Total Liabilities and Shareholders' Equity	25,060	25,012
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	23,322	22,755
CSX Transportation
Current Assets:
Cash and Cash Equivalents	127	175	144	100
Short-term Investments	0	0
Accounts Receivable - Net	182	198
Receivable from Affiliates	2,268	2,038
Materials and Supplies	399	350
Other Current Assets	66	120
Total Current Assets	3,042	2,881
Properties	39,727	38,964
Accumulated Depreciation	(10,343)	(10,016)
Properties - Net	29,384	28,948
Other Long-term Assets	400	399
Total Assets	33,444	32,886
Current Liabilities:
Accounts Payable	633	626
Labor and Fringe Benefits Payable	394	407
Payable to Affiliates	407	437
Casualty, Environmental and Other Reserves	117	115
Current Maturities of Long-term Debt	19	19
Income and Other Taxes Payable	445	183
Other Current Liabilities	148	437
Total Current Liabilities	2,163	2,224
Casualty, Environmental and Other Reserves	197	219
Long-term Debt	780	783
Deferred Income Taxes - Net	9,317	9,141
Other Long-term Liabilities	469	484
Total Liabilities	12,926	12,851
Shareholders' Equity
Common Stock, $1 Par Value	181	181
Other Capital	5,092	5,091
Retained Earnings	15,259	14,774
Accumulated Other Comprehensive Loss	(31)	(31)
Noncontrolling Interest	17	20
Total Shareholders' Equity	20,518	20,035
Total Liabilities and Shareholders' Equity	33,444	32,886
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	618	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	19	9	$ 61	$ 59
Short-term Investments	2	0
Accounts Receivable - Net	731	783
Receivable from Affiliates	(3,356)	(3,130)
Materials and Supplies	0	0
Other Current Assets	16	9
Total Current Assets	(2,588)	(2,329)
Properties	2,617	2,609
Accumulated Depreciation	(1,394)	(1,383)
Properties - Net	1,223	1,226
Other Long-term Assets	(101)	(70)
Total Assets	(23,954)	(23,153)
Current Liabilities:
Accounts Payable	25	30
Labor and Fringe Benefits Payable	34	47
Payable to Affiliates	(3,711)	(3,391)
Casualty, Environmental and Other Reserves	16	16
Current Maturities of Long-term Debt	0	0
Income and Other Taxes Payable	26	12
Other Current Liabilities	2	2
Total Current Liabilities	(3,608)	(3,284)
Casualty, Environmental and Other Reserves	49	50
Long-term Debt	0	0
Deferred Income Taxes - Net	235	226
Other Long-term Liabilities	(125)	(126)
Total Liabilities	(3,449)	(3,134)
Shareholders' Equity
Common Stock, $1 Par Value	(181)	(181)
Other Capital	(5,092)	(5,091)
Retained Earnings	(15,259)	(14,774)
Accumulated Other Comprehensive Loss	31	31
Noncontrolling Interest	(4)	(4)
Total Shareholders' Equity	(20,505)	(20,019)
Total Liabilities and Shareholders' Equity	(23,954)	(23,153)
Eliminations and Other | Investments in Conrail
Current Assets:
Investment in Affiliates and Consolidated Subsidiaries	818	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	$ (23,322)	$ (22,755)