Segment and Geographic Information - Summarized Balance Sheet Information of Reportable Segments (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 24.9	$ 27.2	$ 35.7
Trade accounts receivable, net	122.5	88.4
Financing receivable	16.5	28.4
Inventories	107.3	118.2
Prepaid expenses, supplies and other current assets	33.9	24.6
Total current assets	305.1	286.8
Property, plant and equipment, net	247.5	289.2
Equity method investment	7.9	5.0
Identifiable intangible assets, net		12.5
Goodwill	9.8	42.2	104.3
Other noncurrent assets	12.8	9.8
TOTAL ASSETS	592.1	645.5
Current liabilities:
Trade payables	96.4	115.8
Accrued liabilities	28.1	46.4
Total current liabilities	232.0	164.5
Accrued pension benefits	46.9	42.0	38.0
Environmental liabilities	10.4	11.6	11.7
Other noncurrent liabilities	7.4	6.9
Liabilities not subject to compromise	303.8	586.1
Liabilities subject to compromise	340.7
TOTAL LIABILITIES	644.5	586.1
RANA
Current assets:
Goodwill		33.6	95.4
RAEU
Current assets:
Goodwill	9.8	8.6	$ 8.9
Operating Segments | RANA
Current assets:
Cash and cash equivalents	14.4	11.5
Trade accounts receivable, net	105.3	76.2
Inventories	71.5	79.3
Prepaid expenses, supplies and other current assets	23.6	13.7
Total current assets	214.8	180.7
Property, plant and equipment, net	141.9	195.0
Equity method investment	7.9	5.0
Identifiable intangible assets, net		12.5
Goodwill		33.6
Other noncurrent assets	8.8	5.0
TOTAL ASSETS	373.4	431.8
Current liabilities:
Trade payables	60.3	73.8
Accrued liabilities	15.1	30.0
Total current liabilities	75.4	103.8
Environmental liabilities	10.4	11.6
Other noncurrent liabilities	5.6	4.5
Liabilities not subject to compromise	91.4	119.9
Liabilities subject to compromise	337.6
TOTAL LIABILITIES	429.0	119.9
Operating Segments | RAEU
Current assets:
Cash and cash equivalents	8.5	5.7
Trade accounts receivable, net	17.2	12.2
Financing receivable	16.5	28.4
Inventories	35.8	38.9
Prepaid expenses, supplies and other current assets	7.8	6.4
Total current assets	85.8	91.6
Property, plant and equipment, net	105.5	94.2
Goodwill	9.8	8.6
Other noncurrent assets	3.3	3.5
TOTAL ASSETS	204.4	197.9
Current liabilities:
Trade payables	36.1	41.8
Accrued liabilities	12.2	13.4
Total current liabilities	48.3	55.2
Accrued pension benefits	46.9	42.0
Other noncurrent liabilities	1.9	1.8
Liabilities not subject to compromise	97.1	99.0
TOTAL LIABILITIES	$ 97.1	$ 99.0