Supplemental Condensed Consolidating Financial Information - Consolidating Balance Sheet (Details) - USD ($) $ / shares in Units, $ in Millions	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Assets
Cash and cash equivalents	$ 136.7	$ 134.0	$ 108.0	$ 123.4
Receivables	65.3	60.7
Receivable from redemption of Brazilian investment	0.0	20.5
Inventories	116.4	92.5
Income tax receivable	16.5	4.6
Other current assets	6.1	3.8
Advances to affiliate	0.0	0.0
Total current assets	341.0	316.1
Notes receivable from affiliate	0.0	0.0
Properties, plants and equipment, net	1,510.9	1,542.6
Goodwill	76.9	76.9
Other intangible assets, net	173.5	179.0
Deferred charges and other assets	4.5	6.3
Investment in subsidiaries	0.0	0.0
Total assets	2,106.8	2,120.9
Liabilities and Equity
Advances from affiliate	0.0	0.0
Accounts payable	126.4	98.6
Accrued liabilities	43.6	49.8
Deferred revenue	12.0	2.5
Current portion of long-term debt and financing obligation	3.7	4.9
Interest payable	6.6	16.2
Income taxes payable	0.0	0.0
Total current liabilities	192.3	172.0
Long-term debt and financing obligation	870.3	849.2
Payable to affiliate	0.0	0.0
Accrual for black lung benefits	46.0	45.4
Retirement benefit liabilities	27.8	29.0
Deferred income taxes	428.7	352.5
Asset retirement obligations	13.9	13.9
Other deferred credits and liabilities	20.4	19.0
Total liabilities	1,599.4	1,481.0
Equity
Preferred stock, $0.01 par value. Authorized 50,000,000 shares; no issued shares at June 30, 2017 and December 31, 2016	0.0	0.0
Common stock, $0.01 par value. Authorized 300,000,000 shares; issued 71,807,075 and 71,707,304 shares at June 30, 2017 and December 31, 2016, respectively	0.7	0.7
Treasury stock, 7,477,657 shares at June 30, 2017 and December 31, 2016, respectively	(140.7)	(140.7)
Additional paid-in capital	489.2	492.1
Accumulated other comprehensive loss	(19.2)	(19.0)
Retained deficit	(45.5)	(22.0)
Total SunCoke Energy, Inc. stockholders’ equity	284.5	311.1
Noncontrolling interests	222.9	328.8
Total equity	507.4	639.9
Total liabilities and equity	$ 2,106.8	$ 2,120.9
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)	71,807,075	71,707,304
Treasury stock, shares (in shares)	7,477,657	7,477,657
Reportable Legal Entities | Issuer
Assets
Cash and cash equivalents	$ 0.0	$ 0.0	0.0	0.0
Receivables	0.0	0.0
Receivable from redemption of Brazilian investment		0.0
Inventories	0.0	0.0
Income tax receivable	0.0	17.8
Other current assets	0.0	0.2
Advances to affiliate	0.0	0.0
Total current assets	0.0	18.0
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 charges and other assets	0.0	0.0
Investment in subsidiaries	519.8	542.7
Total assets	519.8	560.7
Liabilities and Equity
Advances from affiliate	165.3	184.2
Accounts payable	0.0	0.0
Accrued liabilities	0.8	1.7
Deferred revenue	0.0	0.0
Current portion of long-term debt and financing obligation	0.0	0.0
Interest payable	1.4	1.5
Income taxes payable	0.8	0.0
Total current liabilities	168.3	187.4
Long-term debt and financing obligation	42.5	43.5
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	21.3	15.9
Asset retirement obligations	0.0	0.0
Other deferred credits and liabilities	3.2	2.8
Total liabilities	235.3	249.6
Equity
Preferred stock, $0.01 par value. Authorized 50,000,000 shares; no issued shares at June 30, 2017 and December 31, 2016	0.0	0.0
Common stock, $0.01 par value. Authorized 300,000,000 shares; issued 71,807,075 and 71,707,304 shares at June 30, 2017 and December 31, 2016, respectively	0.7	0.7
Treasury stock, 7,477,657 shares at June 30, 2017 and December 31, 2016, respectively	(140.7)	(140.7)
Additional paid-in capital	489.2	492.1
Accumulated other comprehensive loss	(19.2)	(19.0)
Retained deficit	(45.5)	(22.0)
Total SunCoke Energy, Inc. stockholders’ equity	284.5	311.1
Noncontrolling interests	0.0	0.0
Total equity	284.5	311.1
Total liabilities and equity	519.8	560.7
Reportable Legal Entities | Guarantor Subsidiaries
Assets
Cash and cash equivalents	94.5	59.7	33.0	70.6
Receivables	11.3	12.2
Receivable from redemption of Brazilian investment		0.0
Inventories	10.9	9.0
Income tax receivable	0.0	0.0
Other current assets	3.0	1.8
Advances to affiliate	239.8	282.2
Total current assets	359.5	364.9
Notes receivable from affiliate	89.0	89.0
Properties, plants and equipment, net	61.1	62.8
Goodwill	3.4	3.4
Other intangible assets, net	2.0	2.3
Deferred charges and other assets	3.5	5.1
Investment in subsidiaries	731.2	688.2
Total assets	1,249.7	1,215.7
Liabilities and Equity
Advances from affiliate	0.0	0.0
Accounts payable	17.0	13.6
Accrued liabilities	15.9	20.5
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	65.9	87.5
Total current liabilities	98.8	121.6
Long-term debt and financing obligation	0.0	0.0
Payable to affiliate	300.0	300.0
Accrual for black lung benefits	12.7	12.3
Retirement benefit liabilities	13.6	14.1
Deferred income taxes	278.3	371.0
Asset retirement obligations	0.0	0.0
Other deferred credits and liabilities	6.8	6.4
Total liabilities	710.2	825.4
Equity
Preferred stock, $0.01 par value. Authorized 50,000,000 shares; no issued shares at June 30, 2017 and December 31, 2016	0.0	0.0
Common stock, $0.01 par value. Authorized 300,000,000 shares; issued 71,807,075 and 71,707,304 shares at June 30, 2017 and December 31, 2016, respectively	0.0	0.0
Treasury stock, 7,477,657 shares at June 30, 2017 and December 31, 2016, respectively	0.0	0.0
Additional paid-in capital	195.4	42.1
Accumulated other comprehensive loss	(1.6)	(1.6)
Retained deficit	345.7	349.8
Total SunCoke Energy, Inc. stockholders’ equity	539.5	390.3
Noncontrolling interests	0.0	0.0
Total equity	539.5	390.3
Total liabilities and equity	1,249.7	1,215.7
Reportable Legal Entities | Non- Guarantor Subsidiaries
Assets
Cash and cash equivalents	42.2	74.3	75.0	52.8
Receivables	54.0	48.5
Receivable from redemption of Brazilian investment		20.5
Inventories	105.5	83.5
Income tax receivable	83.2	74.3
Other current assets	3.1	1.8
Advances to affiliate	0.0	0.0
Total current assets	288.0	302.9
Notes receivable from affiliate	300.0	300.0
Properties, plants and equipment, net	1,449.8	1,479.8
Goodwill	73.5	73.5
Other intangible assets, net	171.5	176.7
Deferred charges and other assets	1.0	1.2
Investment in subsidiaries	0.0	0.0
Total assets	2,283.8	2,334.1
Liabilities and Equity
Advances from affiliate	74.5	98.0
Accounts payable	109.4	85.0
Accrued liabilities	26.9	27.6
Deferred revenue	12.0	2.5
Current portion of long-term debt and financing obligation	3.7	4.9
Interest payable	5.2	14.7
Income taxes payable	0.0	0.0
Total current liabilities	231.7	232.7
Long-term debt and financing obligation	827.8	805.7
Payable to affiliate	89.0	89.0
Accrual for black lung benefits	33.3	33.1
Retirement benefit liabilities	14.2	14.9
Deferred income taxes	129.1	(34.4)
Asset retirement obligations	13.9	13.9
Other deferred credits and liabilities	10.4	9.8
Total liabilities	1,349.4	1,164.7
Equity
Preferred stock, $0.01 par value. Authorized 50,000,000 shares; no issued shares at June 30, 2017 and December 31, 2016	0.0	0.0
Common stock, $0.01 par value. Authorized 300,000,000 shares; issued 71,807,075 and 71,707,304 shares at June 30, 2017 and December 31, 2016, respectively	0.0	0.0
Treasury stock, 7,477,657 shares at June 30, 2017 and December 31, 2016, respectively	0.0	0.0
Additional paid-in capital	654.8	672.2
Accumulated other comprehensive loss	(17.6)	(17.4)
Retained deficit	74.3	185.8
Total SunCoke Energy, Inc. stockholders’ equity	711.5	840.6
Noncontrolling interests	222.9	328.8
Total equity	934.4	1,169.4
Total liabilities and equity	2,283.8	2,334.1
Combining and Consolidating Adjustments
Assets
Cash and cash equivalents	0.0	0.0	$ 0.0	$ 0.0
Receivables	0.0	0.0
Receivable from redemption of Brazilian investment		0.0
Inventories	0.0	0.0
Income tax receivable	(66.7)	(87.5)
Other current assets	0.0	0.0
Advances to affiliate	(239.8)	(282.2)
Total current assets	(306.5)	(369.7)
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 charges and other assets	0.0	0.0
Investment in subsidiaries	(1,251.0)	(1,230.9)
Total assets	(1,946.5)	(1,989.6)
Liabilities and Equity
Advances from affiliate	(239.8)	(282.2)
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	(66.7)	(87.5)
Total current liabilities	(306.5)	(369.7)
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	0.0	0.0
Asset retirement obligations	0.0	0.0
Other deferred credits and liabilities	0.0	0.0
Total liabilities	(695.5)	(758.7)
Equity
Preferred stock, $0.01 par value. Authorized 50,000,000 shares; no issued shares at June 30, 2017 and December 31, 2016	0.0	0.0
Common stock, $0.01 par value. Authorized 300,000,000 shares; issued 71,807,075 and 71,707,304 shares at June 30, 2017 and December 31, 2016, respectively	0.0	0.0
Treasury stock, 7,477,657 shares at June 30, 2017 and December 31, 2016, respectively	0.0	0.0
Additional paid-in capital	(850.2)	(714.3)
Accumulated other comprehensive loss	19.2	19.0
Retained deficit	(420.0)	(535.6)
Total SunCoke Energy, Inc. stockholders’ equity	(1,251.0)	(1,230.9)
Noncontrolling interests	0.0	0.0
Total equity	(1,251.0)	(1,230.9)
Total liabilities and equity	$ (1,946.5)	$ (1,989.6)