Segment and Geographic Information - Schedule of Revenues and Segment Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Revenues	$ 3,375.9	$ 3,445.9	$ 2,857.3
Segment assets	2,712.2	2,779.4
Payments for property, plant and equipment	125.7	108.2	207.7
North America
Segment Reporting Information [Line Items]
Revenues	1,935.0	1,915.7	1,467.8
Europe
Segment Reporting Information [Line Items]
Revenues	1,254.3	1,382.2	1,272.6
Asia Pacific
Segment Reporting Information [Line Items]
Revenues	186.6	148.0	116.9
Operating Segments
Segment Reporting Information [Line Items]
Segment income	433.9	349.4	230.4
Segment assets	2,533.1	2,536.6
Payments for property, plant and equipment	124.1	106.4	206.3
Operating Segments \| North America
Segment Reporting Information [Line Items]
Revenues	1,935.0	1,915.7	1,467.8
Segment income	259.8	196.0	88.0
Segment assets	1,467.7	1,460.0
Payments for property, plant and equipment	(67.6)	60.2	174.6
Operating Segments \| Europe
Segment Reporting Information [Line Items]
Revenues	1,275.9	1,407.4	1,300.7
Segment income	130.1	129.8	127.4
Segment assets	719.7	736.4
Payments for property, plant and equipment	(41.2)	34.2	25.8
Operating Segments \| Asia Pacific
Segment Reporting Information [Line Items]
Revenues	186.6	148.8	122.3
Segment income	44.0	23.6	15.0
Segment assets	345.7	340.2
Payments for property, plant and equipment	(15.3)	12.0	5.9
Intra - entity Revenues
Segment Reporting Information [Line Items]
Revenues	(21.6)	(26.0)	(33.5)
Intra - entity Revenues \| North America
Segment Reporting Information [Line Items]
Revenues	0.0	0.0	0.0
Intra - entity Revenues \| Europe
Segment Reporting Information [Line Items]
Revenues	(21.6)	25.2	(28.1)
Intra - entity Revenues \| Asia Pacific
Segment Reporting Information [Line Items]
Revenues	$ 0.0	$ 0.8	$ (5.4)

Aleris Corp 10-K