Supplemental Condensed Consolidating Financial Information - Consolidating Balance Sheet (Details) - USD ($) $ / shares in Units, $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Assets
Cash and cash equivalents	$ 147.0	$ 120.2
Receivables	75.3	68.5
Inventories	110.1	111.0
Income tax receivable	5.4	4.8
Other current assets	9.0	6.7
Advances to affiliate	0.0	0.0
Total current assets	346.8	311.2
Notes receivable from affiliate	0.0	0.0
Properties, plants and equipment, net	1,488.2	1,501.3
Goodwill	76.9	76.9
Other intangible assets, net	165.1	167.9
Deferred income taxes	0.0	0.0
Deferred charges and other assets	3.0	2.8
Total assets	2,080.0	2,060.1
Liabilities and Equity
Advances from affiliate	0.0	0.0
Accounts payable	131.1	115.5
Accrued liabilities	44.3	53.2
Deferred revenue	3.6	1.7
Current portion of long-term debt and financing obligation	3.8	2.6
Interest payable	17.1	5.4
Income taxes payable	0.0	0.0
Total current liabilities	199.9	178.4
Long-term debt and financing obligation	860.2	861.1
Payable to affiliate	0.0	0.0
Accrual for black lung benefits	45.4	44.9
Retirement benefit liabilities	27.7	28.2
Deferred income taxes	257.7	257.8
Asset retirement obligations	14.1	14.0
Other deferred credits and liabilities	15.5	16.1
Total liabilities	1,420.5	1,400.5
Equity
Preferred stock, $0.01 par value. Authorized 50,000,000 shares; no issued shares at both March 31, 2018 and December 31, 2017	0.0	0.0
Common stock, $0.01 par value. Authorized 300,000,000 shares; issued 72,076,092 and 72,006,905 shares at March 31, 2018 and December 31, 2017, respectively	0.7	0.7
Treasury stock, 7,477,657 shares at both March 31, 2018 and December 31, 2017	(140.7)	(140.7)
Additional paid-in capital	486.0	486.2
Accumulated other comprehensive loss	(21.3)	(21.2)
Retained earnings	109.9	101.2
Equity investment eliminations	0.0	0.0
Total SunCoke Energy, Inc. stockholders’ equity	434.6	426.2
Noncontrolling interests	224.9	233.4
Total equity	659.5	659.6
Total liabilities and equity	$ 2,080.0	$ 2,060.1
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)	50,000,000	50,000,000
Preferred stock, shares issued (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	300,000,000	300,000,000
Common stock, shares, issued (in shares)	72,076,092	72,006,905
Treasury stock, shares (in shares)	7,477,657	7,477,657
Reportable Legal Entities | Issuer
Assets
Cash and cash equivalents	$ 0.0	$ 0.0
Receivables	0.0	0.0
Inventories	0.0	0.0
Income tax receivable	0.0	0.0
Other current assets	0.0	0.0
Advances to affiliate	0.0	0.0
Total current assets	0.0	0.0
Notes receivable from affiliate	0.0	0.0
Properties, plants and equipment, net	0.0	0.0
Goodwill	0.0	0.0
Other intangible assets, net	0.0	0.0
Deferred income taxes	7.1	7.1
Deferred charges and other assets	0.0	0.0
Total assets	7.1	7.1
Liabilities and Equity
Advances from affiliate	165.7	162.2
Accounts payable	0.0	0.0
Accrued liabilities	0.9	1.5
Deferred revenue	0.0	0.0
Current portion of long-term debt and financing obligation	1.2	0.0
Interest payable	0.3	1.4
Income taxes payable	1.6	1.9
Total current liabilities	169.7	167.0
Long-term debt and financing obligation	41.8	42.7
Payable to affiliate	0.0	0.0
Accrual for black lung benefits	0.0	0.0
Retirement benefit liabilities	0.0	0.0
Deferred income taxes	0.0	0.0
Asset retirement obligations	0.0	0.0
Other deferred credits and liabilities	3.0	3.7
Total liabilities	214.5	213.4
Equity
Preferred stock, $0.01 par value. Authorized 50,000,000 shares; no issued shares at both March 31, 2018 and December 31, 2017	0.0	0.0
Common stock, $0.01 par value. Authorized 300,000,000 shares; issued 72,076,092 and 72,006,905 shares at March 31, 2018 and December 31, 2017, respectively	0.7	0.7
Treasury stock, 7,477,657 shares at both March 31, 2018 and December 31, 2017	(140.7)	(140.7)
Additional paid-in capital	486.0	486.2
Accumulated other comprehensive loss	(21.3)	(21.2)
Retained earnings	110.0	101.2
Equity investment eliminations	(642.1)	(632.5)
Total SunCoke Energy, Inc. stockholders’ equity	(207.4)	(206.3)
Noncontrolling interests	0.0	0.0
Total equity	(207.4)	(206.3)
Total liabilities and equity	7.1	7.1
Reportable Legal Entities | Guarantor Subsidiaries
Assets
Cash and cash equivalents	93.2	103.6
Receivables	16.1	17.1
Inventories	12.8	9.1
Income tax receivable	0.0	0.0
Other current assets	6.0	4.6
Advances to affiliate	263.9	245.8
Total current assets	392.0	380.2
Notes receivable from affiliate	89.0	89.0
Properties, plants and equipment, net	58.4	59.8
Goodwill	3.4	3.4
Other intangible assets, net	1.5	1.7
Deferred income taxes	0.0	0.0
Deferred charges and other assets	2.5	2.3
Total assets	546.8	536.4
Liabilities and Equity
Advances from affiliate	0.0	0.0
Accounts payable	20.9	16.4
Accrued liabilities	13.8	19.7
Deferred revenue	0.0	0.0
Current portion of long-term debt and financing obligation	0.0	0.0
Interest payable	0.0	0.0
Income taxes payable	83.7	81.4
Total current liabilities	118.4	117.5
Long-term debt and financing obligation	0.0	0.0
Payable to affiliate	300.0	300.0
Accrual for black lung benefits	12.0	11.8
Retirement benefit liabilities	13.5	13.7
Deferred income taxes	193.8	193.8
Asset retirement obligations	0.0	0.0
Other deferred credits and liabilities	6.3	6.4
Total liabilities	644.0	643.2
Equity
Preferred stock, $0.01 par value. Authorized 50,000,000 shares; no issued shares at both March 31, 2018 and December 31, 2017	0.0	0.0
Common stock, $0.01 par value. Authorized 300,000,000 shares; issued 72,076,092 and 72,006,905 shares at March 31, 2018 and December 31, 2017, respectively	0.0	0.0
Treasury stock, 7,477,657 shares at both March 31, 2018 and December 31, 2017	0.0	0.0
Additional paid-in capital	77.5	141.0
Accumulated other comprehensive loss	(2.2)	(2.2)
Retained earnings	489.8	475.6
Equity investment eliminations	(662.3)	(721.2)
Total SunCoke Energy, Inc. stockholders’ equity	(97.2)	(106.8)
Noncontrolling interests	0.0	0.0
Total equity	(97.2)	(106.8)
Total liabilities and equity	546.8	536.4
Reportable Legal Entities | Non- Guarantor Subsidiaries
Assets
Cash and cash equivalents	53.8	16.6
Receivables	59.2	51.4
Inventories	97.3	101.9
Income tax receivable	90.7	88.1
Other current assets	3.0	2.1
Advances to affiliate	0.0	0.0
Total current assets	304.0	260.1
Notes receivable from affiliate	300.0	300.0
Properties, plants and equipment, net	1,429.8	1,441.5
Goodwill	73.5	73.5
Other intangible assets, net	163.6	166.2
Deferred income taxes	0.0	0.0
Deferred charges and other assets	0.5	0.5
Total assets	2,271.4	2,241.8
Liabilities and Equity
Advances from affiliate	98.2	83.6
Accounts payable	110.2	99.1
Accrued liabilities	29.6	32.0
Deferred revenue	3.6	1.7
Current portion of long-term debt and financing obligation	2.6	2.6
Interest payable	16.8	4.0
Income taxes payable	0.0	0.0
Total current liabilities	261.0	223.0
Long-term debt and financing obligation	818.4	818.4
Payable to affiliate	89.0	89.0
Accrual for black lung benefits	33.4	33.1
Retirement benefit liabilities	14.2	14.5
Deferred income taxes	71.0	71.1
Asset retirement obligations	14.1	14.0
Other deferred credits and liabilities	6.2	6.0
Total liabilities	1,307.3	1,269.1
Equity
Preferred stock, $0.01 par value. Authorized 50,000,000 shares; no issued shares at both March 31, 2018 and December 31, 2017	0.0	0.0
Common stock, $0.01 par value. Authorized 300,000,000 shares; issued 72,076,092 and 72,006,905 shares at March 31, 2018 and December 31, 2017, respectively	0.0	0.0
Treasury stock, 7,477,657 shares at both March 31, 2018 and December 31, 2017	0.0	0.0
Additional paid-in capital	637.7	641.9
Accumulated other comprehensive loss	(19.1)	(19.0)
Retained earnings	120.6	116.4
Equity investment eliminations	0.0	0.0
Total SunCoke Energy, Inc. stockholders’ equity	739.2	739.3
Noncontrolling interests	224.9	233.4
Total equity	964.1	972.7
Total liabilities and equity	2,271.4	2,241.8
Combining and Consolidating Adjustments
Assets
Cash and cash equivalents	0.0	0.0
Receivables	0.0	0.0
Inventories	0.0	0.0
Income tax receivable	(85.3)	(83.3)
Other current assets	0.0	0.0
Advances to affiliate	(263.9)	(245.8)
Total current assets	(349.2)	(329.1)
Notes receivable from affiliate	(389.0)	(389.0)
Properties, plants and equipment, net	0.0	0.0
Goodwill	0.0	0.0
Other intangible assets, net	0.0	0.0
Deferred income taxes	(7.1)	(7.1)
Deferred charges and other assets	0.0	0.0
Total assets	(745.3)	(725.2)
Liabilities and Equity
Advances from affiliate	(263.9)	(245.8)
Accounts payable	0.0	0.0
Accrued liabilities	0.0	0.0
Deferred revenue	0.0	0.0
Current portion of long-term debt and financing obligation	0.0	0.0
Interest payable	0.0	0.0
Income taxes payable	(85.3)	(83.3)
Total current liabilities	(349.2)	(329.1)
Long-term debt and financing obligation	0.0	0.0
Payable to affiliate	(389.0)	(389.0)
Accrual for black lung benefits	0.0	0.0
Retirement benefit liabilities	0.0	0.0
Deferred income taxes	(7.1)	(7.1)
Asset retirement obligations	0.0	0.0
Other deferred credits and liabilities	0.0	0.0
Total liabilities	(745.3)	(725.2)
Equity
Preferred stock, $0.01 par value. Authorized 50,000,000 shares; no issued shares at both March 31, 2018 and December 31, 2017	0.0	0.0
Common stock, $0.01 par value. Authorized 300,000,000 shares; issued 72,076,092 and 72,006,905 shares at March 31, 2018 and December 31, 2017, respectively	0.0	0.0
Treasury stock, 7,477,657 shares at both March 31, 2018 and December 31, 2017	0.0	0.0
Additional paid-in capital	(715.2)	(782.9)
Accumulated other comprehensive loss	21.3	21.2
Retained earnings	(610.5)	(592.0)
Equity investment eliminations	1,304.4	1,353.7
Total SunCoke Energy, Inc. stockholders’ equity	0.0	0.0
Noncontrolling interests	0.0	0.0
Total equity	0.0	0.0
Total liabilities and equity	$ (745.3)	$ (725.2)