Acquisitions (Narrative) (Details) - USD ($) $ in Millions			3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 28, 2019	Jun. 27, 2019	Jun. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Subsidiary, Sale of Stock [Line Items]
Accrued Simplification Transaction costs			$ 6.4	$ 6.4	$ 0.0
Simplification Transaction
Subsidiary, Sale of Stock [Line Items]
Outstanding Partnership public units (in shares)	17,727,249
Units purchased (in shares)	24,818,149			25,453,651
Quarterly distribution of newly issued shares (in shares)	635,502
Transaction costs			4.4	$ 4.9	$ 0.4
Simplification Transaction | Additional Paid-In Capital
Subsidiary, Sale of Stock [Line Items]
Accrued Simplification Transaction costs			$ 5.4	$ 5.4
Public Unit Purchase Program
Subsidiary, Sale of Stock [Line Items]
Units purchased (in shares)			42,706	231,171
Suncoke Inc
Subsidiary, Sale of Stock [Line Items]
Ownership interest of general partnership (as a percent)		60.40%
Interest in partnership (as a percent)		2.00%
Suncoke Inc | Simplification Transaction
Subsidiary, Sale of Stock [Line Items]
Ownership interest of general partnership (as a percent)	100.00%
Public Unitholders
Subsidiary, Sale of Stock [Line Items]
Ownership interest, public (as a percent)		37.60%