Summarized Consolidating Financial Data - Consolidating Balance Sheet (Details) - USD ($) $ / shares in Units, $ in Millions	Sep. 23, 2016	Dec. 25, 2015	Sep. 25, 2015	Dec. 26, 2014
Current Assets:
Cash and Cash Equivalents	$ 603	$ 628	$ 541	$ 669
Short-term Investments	152	810
Accounts Receivable - Net	925	982
Receivable from Affiliates	0	0
Materials and Supplies	397	350
Other Current Assets	86	70
Total Current Assets	2,163	2,840
Properties	42,720	41,574
Accumulated Depreciation	(11,938)	(11,400)
Properties - Net	30,782	30,174
Other Long-term Assets	303	337
Total Assets	34,681	34,745
Current Liabilities:
Accounts Payable	859	764
Labor and Fringe Benefits Payable	450	490
Payable to Affiliates	0	0
Casualty, Environmental and Other Reserves	124	131
Current Maturities of Long-term Debt	631	20
Income and Other Taxes Payable	90	108
Other Current Liabilities	109	439
Total Current Liabilities	2,263	1,952
Casualty, Environmental and Other Reserves	250	269
Long-term Debt	9,888	10,515
Deferred Income Taxes - Net	9,505	9,179
Other Long-term Liabilities	1,105	1,162
Total Liabilities	23,011	23,077
Shareholders' Equity
Common Stock, $1 Par Value	937	966
Other Capital	125	113
Retained Earnings	11,233	11,238
Accumulated Other Comprehensive Loss	(639)	(665)
Noncontrolling Interest	14	16
Total Shareholders' Equity	11,670	11,668
Total Liabilities and Shareholders' Equity	$ 34,681	$ 34,745
Common stock, par value (in dollars per share)	$ 1	$ 1
Investments in Conrail
Current Assets:
Investment in Affiliates and Other Companies	$ 830	$ 803
Affiliates and Other Companies
Current Assets:
Investment in Affiliates and Other Companies	603	591
Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Other Companies	0	0
CSX Corporation
Current Assets:
Cash and Cash Equivalents	448	444	311	510
Short-term Investments	150	810
Accounts Receivable - Net	(3)	1
Receivable from Affiliates	1,158	1,092
Materials and Supplies	0	0
Other Current Assets	11	(59)
Total Current Assets	1,764	2,288
Properties	1	1
Accumulated Depreciation	(1)	(1)
Properties - Net	0	0
Other Long-term Assets	3	8
Total Assets	25,406	25,012
Current Liabilities:
Accounts Payable	150	108
Labor and Fringe Benefits Payable	36	36
Payable to Affiliates	3,601	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	4,066	3,012
Casualty, Environmental and Other Reserves	0	0
Long-term Debt	9,127	9,732
Deferred Income Taxes - Net	(206)	(188)
Other Long-term Liabilities	763	804
Total Liabilities	13,750	13,360
Shareholders' Equity
Common Stock, $1 Par Value	937	966
Other Capital	125	113
Retained Earnings	11,233	11,238
Accumulated Other Comprehensive Loss	(639)	(665)
Noncontrolling Interest	0	0
Total Shareholders' Equity	11,656	11,652
Total Liabilities and Shareholders' Equity	25,406	25,012
CSX Corporation | Investments in Conrail
Current Assets:
Investment in Affiliates and Other Companies	0	0
CSX Corporation | Affiliates and Other Companies
Current Assets:
Investment in Affiliates and Other Companies	(39)	(39)
CSX Corporation | Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Other Companies	23,678	22,755
CSX Transportation
Current Assets:
Cash and Cash Equivalents	130	175	168	100
Short-term Investments	0	0
Accounts Receivable - Net	197	198
Receivable from Affiliates	2,504	2,038
Materials and Supplies	397	350
Other Current Assets	56	120
Total Current Assets	3,284	2,881
Properties	40,052	38,964
Accumulated Depreciation	(10,508)	(10,016)
Properties - Net	29,544	28,948
Other Long-term Assets	403	399
Total Assets	33,859	32,886
Current Liabilities:
Accounts Payable	679	626
Labor and Fringe Benefits Payable	371	407
Payable to Affiliates	445	437
Casualty, Environmental and Other Reserves	109	115
Current Maturities of Long-term Debt	19	19
Income and Other Taxes Payable	394	183
Other Current Liabilities	107	437
Total Current Liabilities	2,124	2,224
Casualty, Environmental and Other Reserves	202	219
Long-term Debt	761	783
Deferred Income Taxes - Net	9,470	9,141
Other Long-term Liabilities	468	484
Total Liabilities	13,025	12,851
Shareholders' Equity
Common Stock, $1 Par Value	181	181
Other Capital	5,094	5,091
Retained Earnings	15,575	14,774
Accumulated Other Comprehensive Loss	(30)	(31)
Noncontrolling Interest	14	20
Total Shareholders' Equity	20,834	20,035
Total Liabilities and Shareholders' Equity	33,859	32,886
CSX Transportation | Investments in Conrail
Current Assets:
Investment in Affiliates and Other Companies	0	0
CSX Transportation | Affiliates and Other Companies
Current Assets:
Investment in Affiliates and Other Companies	628	658
CSX Transportation | Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Other Companies	0	0
Eliminations and Other
Current Assets:
Cash and Cash Equivalents	25	9	$ 62	$ 59
Short-term Investments	2	0
Accounts Receivable - Net	731	783
Receivable from Affiliates	(3,662)	(3,130)
Materials and Supplies	0	0
Other Current Assets	19	9
Total Current Assets	(2,885)	(2,329)
Properties	2,667	2,609
Accumulated Depreciation	(1,429)	(1,383)
Properties - Net	1,238	1,226
Other Long-term Assets	(103)	(70)
Total Assets	(24,584)	(23,153)
Current Liabilities:
Accounts Payable	30	30
Labor and Fringe Benefits Payable	43	47
Payable to Affiliates	(4,046)	(3,391)
Casualty, Environmental and Other Reserves	15	16
Current Maturities of Long-term Debt	(1)	0
Income and Other Taxes Payable	30	12
Other Current Liabilities	2	2
Total Current Liabilities	(3,927)	(3,284)
Casualty, Environmental and Other Reserves	48	50
Long-term Debt	0	0
Deferred Income Taxes - Net	241	226
Other Long-term Liabilities	(126)	(126)
Total Liabilities	(3,764)	(3,134)
Shareholders' Equity
Common Stock, $1 Par Value	(181)	(181)
Other Capital	(5,094)	(5,091)
Retained Earnings	(15,575)	(14,774)
Accumulated Other Comprehensive Loss	30	31
Noncontrolling Interest	0	(4)
Total Shareholders' Equity	(20,820)	(20,019)
Total Liabilities and Shareholders' Equity	(24,584)	(23,153)
Eliminations and Other | Investments in Conrail
Current Assets:
Investment in Affiliates and Other Companies	830	803
Eliminations and Other | Affiliates and Other Companies
Current Assets:
Investment in Affiliates and Other Companies	14	(28)
Eliminations and Other | Investments in Consolidated Subsidiaries
Current Assets:
Investment in Affiliates and Other Companies	$ (23,678)	$ (22,755)