Employee Benefit Plans (Tables)

12 Months Ended

Dec. 31, 2017

Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]

Summary of Participants

In order to perform this valuation, the actuaries are provided with the details of the population covered at the beginning of the year, summarized in the table below, and projects that population forward to the end of the year.

	Summary of Participants as of
	January 1, 2017
	Pension Plans	Post-retirement Medical Plan
Active Employees	3,744	458
Retirees and Beneficiaries	12,723	9,940
Other(a)	3,591	36
Total	20,058	10,434

(a) For pension plans, the other category consists mostly of terminated but vested former employees.  For post-retirement plans, the other category consists of employees on long-term disability that have not yet retired.

Schedule of Future Expected Benefit Payments

Future expected benefit payments are as follows:

	Expected Cash Flows
(Dollars in Millions)	Pension Benefits		Post-retirement Benefits
2018	$	198	$	38
2019	193		28
2020	189		26
2021	186		24
2022	183		22
2023-2026	888		76
Total	$	1,837	$	214

Schedule of Allocation of Plan Assets

The distribution of pension plan assets as of the measurement date is shown in the table below, and these assets are reported net of pension liabilities on the balance sheet.

	December 2017				December 2016
			Percent of				Percent of
(Dollars in Millions)	Amount		Total Assets		Amount		Total Assets
Equity	$	2,060	73	%	$	1,806	71	%
Fixed Income	729		26		665		26
Cash and Cash Equivalents	44		1		68		3
Total	$	2,833	100	%	$	2,539	100	%

Schedule of Changes in Benefit Obligation and Fair Value of Plan Assets

Changes in benefit obligation and the fair value of plan assets for the 2017 and 2016 calendar plan years are as follows:

	Pension Benefits						Post-retirement Benefits
	Plan Year			Plan Year			Plan Year			Plan Year
(Dollars in Millions)	2017			2016			2017			2016
Actuarial Present Value of Benefit Obligation
Accumulated Benefit Obligation	$	2,873		$	2,717		N/A			N/A
Projected Benefit Obligation	3,002			2,871			$	250		$	274
Change in Projected Benefit Obligation:
Projected Benefit Obligation atBeginning of Plan Year	$	2,871		$	2,860		$	274		$	314
Service Cost	36			48			2			2
Interest Cost	92			119			7			12
Plan Participants' Contributions	—			—			7			6
Workforce Reduction Program/Curtailment	58			—			13			—
Actuarial Loss (Gain)	163			20			(17		)	(22		)
Benefits Paid	(218		)	(176		)	(36		)	(38		)
Benefit Obligation at End of Plan Year	$	3,002		$	2,871		$	250		$	274
Change in Plan Assets:
Fair Value of Plan Assets at Beginning of Plan Year	$	2,539		$	2,309		$	—		$	—
Actual Return on Plan Assets	467			139			—			—
Qualified Employer Contributions	—			250			—			—
Non-qualified Employer Contributions	45			17			29			32
Plan Participants' Contributions	—			—			7			6
Benefits Paid	(218		)	(176		)	(36		)	(38		)
Fair Value of Plan Assets at End of Plan Year	2,833			2,539			—			—
Funded Status at End of Plan Year	$	(169	)	$	(332	)	$	(250	)	$	(274	)

Schedule of Amount Recognized in Balance Sheet

Amounts related to pension and post-retirement benefits recorded in other long-term assets, labor and fringe benefits payable and other long-term liabilities on the balance sheet are as follows:

	Pension Benefits						Post-retirement Benefits
	December			December			December			December
(Dollars in Millions)	2017			2016			2017			2016
Amounts Recorded in Consolidated
Balance Sheets:
Long-term Assets (a)	$	57		$	9		$	—		$	—
Current Liabilities	(15		)	(15		)	(38		)	(39		)
Long-term Liabilities	(211		)	(326		)	(212		)	(235		)
Net Amount Recognized in
Consolidated Balance Sheets	$	(169	)	$	(332	)	$	(250	)	$	(274	)

(a) Long-term assets as of December 2017 and 2016 relate to qualified pension plans where assets exceed projected benefit obligations.

Benefit Obligations in Excess of Plan Assets

At December 2017, benefit obligations of the unfunded CSX non-qualified pension plans is disclosed below.

	Aggregate
(Dollars in Millions)	Fair Value		Aggregate
Benefit Obligations in Excess of Plan Assets	of Plan Assets		Benefit Obligation
Projected Benefit Obligation	$	—	$	(226	)
Accumulated Benefit Obligation	—		(216		)

Schedule of Net Benefit Expense

The following table describes the components of expense/(income) related to net benefit expense recorded in labor and fringe on the income statement.

	Pension Benefits Fiscal Years									Post-retirement Benefits Fiscal Years
(Dollars in Millions)	2017			2016			2015			2017		2016		2015
Service Cost	$	36		$	48		$	45		$	2	$	2	$	2
Interest Cost	92			119			116			7		12		12
Expected Return on Plan Assets	(171		)	(157		)	(162		)	—		—		—
Amortization of Net Loss	41			48			70			—		3		4
Amortization of Prior Service Cost	—			—			—			—		—		(1		)
Net Periodic Benefit Expense	(2		)	58			69			9		17		17
Special Termination Benefits - Workforce Reduction Program/Curtailment	60			—			7			13		—		—
Settlement Loss (Gain)	11			(1		)	(2		)	—		—		—
Total Expense	$	69		$	57		$	74		$	22	$	17	$	17

Schedule of Pre-tax Change in Other Comprehensive Loss (Income)

The following table shows the pre-tax change in other comprehensive loss (income) attributable to the components of net expense and the change in benefit obligation for CSX for pension and other post-employment benefits.

(Dollars in Millions)	Pension Benefits						Post-retirement Benefits
Components of Other Comprehensive	December			December			December			December
Loss (Income)	2017			2016			2017			2016
Recognized in the balance sheet
(Gains) Losses	$	(131	)	$	38		$	(17	)	$	(22	)
Expense (Income) recognized in the income statement
Amortization of net losses (a)	$	41		$	48		$	—		$	3
Settlement gain	11			(1		)	—			—
Curtailment loss	4			—			—			—

(a) Amortization of net losses estimated to be expensed for 2018 is approximately $43 million for pension benefits.

Schedule of Pre-tax Amounts to be Amortized that are Included in Accumulated Other Comprehensive Loss

As of December 2017, the balances of pre-tax losses to be amortized related to the Company's pension and post-retirement obligations are $705 million and $7 million, respectively. These amounts are included in accumulated other comprehensive loss, a component of shareholders’ equity.

Schedule of Weighted-Average Assumptions Used

The weighted averages of assumptions used by the Company to value its pension and post-retirement obligations were as follows:

	Pension Benefits					Post-retirement Benefits
	2017			2016		2017			2016
Expected Long-term Return on Plan Assets:
Benefit Cost for Current Plan Year	6.75	%		7.00	%	N/A			N/A
Benefit Cost for Subsequent Plan Year	6.75	%		6.75	%	N/A			N/A
Discount Rates:
Benefit Cost for Plan Year	—	%		—	%	—	%		—	%
Service Cost for Plan Year	4.26	%	(a)	4.30	%	4.11	%	(b)	3.85	%
Interest Cost for Plan Year	3.26	%	(a)	4.30	%	2.78	%	(b)	3.85	%
Benefit Obligation at End of Plan Year	3.56	%		4.08	%	3.34	%		3.71	%
Salary Scale Inflation	4.60	%		4.60	%	N/A			N/A

(a) The pension benefits service cost and interest cost for 2017 were based on a weighted average discount rate of 4.35% and 3.37%, respectively, prior to the management workforce reduction program initiated in 2017 and were reduced to 4.26% and 3.26%, respectively, after the Company remeasured the pension benefits obligation and pension plan assets in the second quarter of 2017.

(b) The post-retirement benefits service cost and interest cost for 2017 were based on a weighted average discount rate of 4.20% and 2.88%, respectively, prior to the management workforce reduction program initiated in 2017 and were reduced to 4.11% and 2.78%, respectively, after the Company remeasured the other post-retirement benefits obligation in the first quarter of 2017.