Non-operating Income (Expense) (Tables)

12 Months Ended

Dec. 31, 2018

Nonoperating Income (Expense) [Abstract]

Schedule of Other Nonoperating Income (Expense) [Table Text Block]

	Year ended December 31,
Dollar amounts in millions	2018			2017			2016
Interest expense	$	(19.0	)	$	(20.6	)	$	(32.9	)
Amortization of debt charges	(0.8		)	(0.9		)	(1.1		)
Capitalized interest	4.0			2.2			1.9
Interest expense, net of capitalized interest	(15.8		)	(19.3		)	(32.1		)
Interest income	18.1			9.5			8.0
Gain on securities	0.4			—			—
SERP market adjustments	(0.9		)	1.0			0.2
Investment income	17.6			10.5			8.2
Net periodic pension cost, excluding service cost	(4.3		)	(9.4		)	(6.2		)
Foreign currency losses	0.4			(4.4		)	2.1
Early debt extinguishment	—			—			(17.3		)
Other non-operating income (expense)	(3.9		)	(13.8		)	(21.4		)
Total non-operating income (expense)	$	(2.1	)	$	(22.6	)	$	(45.3	)