Inventories (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Inventories
LIFO inventories - cost on FIFO method	$ 1,737.3	$ 1,390.0
Cost on FIFO method higher than LIFO value	(293.6)	(21.8)
Inventories - stated on LIFO method	1,443.7	1,368.2
Inventories - stated on FIFO method	373.4	357.8
Inventories	1,817.1	1,726.0
LIFO inventory valuation reserve adjustment charge (income)	$ 271.8	$ 73.3	$ (8.5)