Inventories (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Inventories
LIFO inventories - cost on the FIFO method	$ 1,219.0	$ 1,157.5
LIFO inventory valuation reserve adjustment	51.5	43.0
Lower of cost or market adjustment	(42.6)	(69.1)
Cost on FIFO method lower (higher) than LIFO value	8.9	(26.1)
Inventories - stated on LIFO method	1,227.9	1,131.4
Inventories - stated on FIFO method	304.7	304.6
Inventories	1,532.6	1,436.0
Lower of cost or market charge related to inventories measured using the LIFO method	7.6
LIFO inventory valuation reserve adjustment (income) charge	$ (8.5)	(186.1)	$ 54.5
Liquidation of LIFO inventory quantities that increased cost of sales		$ 38.7