Supplemental Guarantor Condensed Consolidating Financial Statements - Condensed Consolidating Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents	$ 532.0	$ 476.4
Accounts receivable, net	815.4	966.5
Intercompany receivables	0.0	0.0
Inventories, net	373.6	459.7
Other current assets	136.8	127.2
Total current assets	1,857.8	2,029.8
Property, plant and equipment, net	2,358.4	2,514.4
Goodwill	699.1	1,141.8	$ 1,654.3
Other intangible assets, net	864.5	1,111.1
Intercompany notes and accounts receivable	0.0	0.0
Other assets and deferred charges	864.8	713.6
Investment in subsidiaries	0.0	0.0
Total assets	6,644.6	7,510.7	$ 7,882.8
Current liabilities
Current portion of long-term debt	28.7	121.6
Accounts payable	623.5	840.2
Intercompany payables	0.0	0.0
Other current liabilities	374.2	395.0
Total current liabilities	1,026.4	1,356.8
Intercompany notes and accounts payable	0.0	0.0
Long-term debt, net	3,612.3	3,686.8
Other long-term liabilities	1,025.5	980.8
Total liabilities	5,664.2	6,024.4
Total AAM stockholders' equity	977.6	1,483.9
Noncontrolling interests in subsidiaries	2.8	2.4
Total stockholders' equity	980.4	1,486.3
Total liabilities and stockholders' equity	6,644.6	7,510.7
Consolidation, Eliminations [Member]
Current assets
Cash and cash equivalents	0.0	0.0
Accounts receivable, net	0.0	0.0
Intercompany receivables	(8,750.5)	(5,787.0)
Inventories, net	0.0	0.0
Other current assets	0.0	0.0
Total current assets	(8,750.5)	(5,787.0)
Property, plant and equipment, net	0.0	0.0
Goodwill	0.0	0.0
Other intangible assets, net	0.0	0.0
Intercompany notes and accounts receivable	(1,990.6)	(1,461.3)
Other assets and deferred charges	0.0	0.0
Investment in subsidiaries	(5,558.9)	(6,780.7)
Total assets	(16,300.0)	(14,029.0)
Current liabilities
Current portion of long-term debt	0.0	0.0
Accounts payable	0.0	0.0
Intercompany payables	(8,750.5)	(5,787.0)
Other current liabilities	0.0	0.0
Total current liabilities	(8,750.5)	(5,787.0)
Intercompany notes and accounts payable	(1,990.6)	(1,461.3)
Long-term debt, net	0.0	0.0
Other long-term liabilities	0.0	0.0
Total liabilities	(10,741.1)	(7,248.3)
Total AAM stockholders' equity	(5,556.1)	(6,778.3)
Noncontrolling interests in subsidiaries	(2.8)	(2.4)
Total stockholders' equity	(5,558.9)	(6,780.7)
Total liabilities and stockholders' equity	(16,300.0)	(14,029.0)
Holdings [Member]
Current assets
Cash and cash equivalents	0.0	0.0
Accounts receivable, net	0.0	0.0
Intercompany receivables	0.0	0.0
Inventories, net	0.0	0.0
Other current assets	0.0	0.0
Total current assets	0.0	0.0
Property, plant and equipment, net	0.0	0.0
Goodwill	0.0	0.0
Other intangible assets, net	0.0	0.0
Intercompany notes and accounts receivable	0.0	0.0
Other assets and deferred charges	0.0	0.0
Investment in subsidiaries	2,294.0	2,790.5
Total assets	2,294.0	2,790.5
Current liabilities
Current portion of long-term debt	0.0	0.0
Accounts payable	0.0	0.0
Intercompany payables	0.0	0.0
Other current liabilities	0.0	0.0
Total current liabilities	0.0	0.0
Intercompany notes and accounts payable	1,313.6	1,304.2
Long-term debt, net	0.0	0.0
Other long-term liabilities	0.0	0.0
Total liabilities	1,313.6	1,304.2
Total AAM stockholders' equity	977.6	1,483.9
Noncontrolling interests in subsidiaries	2.8	2.4
Total stockholders' equity	980.4	1,486.3
Total liabilities and stockholders' equity	2,294.0	2,790.5
AAM Inc. [Member]
Current assets
Cash and cash equivalents	168.7	36.7
Accounts receivable, net	87.1	122.7
Intercompany receivables	4,603.4	3,337.2
Inventories, net	36.6	42.5
Other current assets	47.6	34.4
Total current assets	4,943.4	3,573.5
Property, plant and equipment, net	287.3	275.8
Goodwill	0.0	0.0
Other intangible assets, net	18.1	18.6
Intercompany notes and accounts receivable	1,829.2	1,316.8
Other assets and deferred charges	408.3	319.8
Investment in subsidiaries	1,773.3	2,241.5
Total assets	9,259.6	7,746.0
Current liabilities
Current portion of long-term debt	4.2	100.0
Accounts payable	85.2	94.2
Intercompany payables	3,652.1	2,050.0
Other current liabilities	158.8	169.0
Total current liabilities	3,900.3	2,413.2
Intercompany notes and accounts payable	11.5	12.5
Long-term debt, net	3,523.4	3,578.3
Other long-term liabilities	475.4	508.9
Total liabilities	7,910.6	6,512.9
Total AAM stockholders' equity	1,349.0	1,233.1
Noncontrolling interests in subsidiaries	0.0	0.0
Total stockholders' equity	1,349.0	1,233.1
Total liabilities and stockholders' equity	9,259.6	7,746.0
Guarantor Subsidiaries [Member]
Current assets
Cash and cash equivalents	0.2	0.2
Accounts receivable, net	176.4	287.7
Intercompany receivables	4,024.5	2,356.3
Inventories, net	114.1	157.7
Other current assets	4.2	6.0
Total current assets	4,319.4	2,807.9
Property, plant and equipment, net	543.9	758.6
Goodwill	377.9	719.0
Other intangible assets, net	817.9	1,059.6
Intercompany notes and accounts receivable	161.4	144.5
Other assets and deferred charges	123.8	126.4
Investment in subsidiaries	1,491.6	1,748.7
Total assets	7,835.9	7,364.7
Current liabilities
Current portion of long-term debt	7.4	0.0
Accounts payable	142.7	246.5
Intercompany payables	5,033.8	3,615.7
Other current liabilities	31.0	35.8
Total current liabilities	5,214.9	3,898.0
Intercompany notes and accounts payable	98.9	0.0
Long-term debt, net	0.0	3.0
Other long-term liabilities	282.5	271.7
Total liabilities	5,596.3	4,172.7
Total AAM stockholders' equity	2,239.6	3,192.0
Noncontrolling interests in subsidiaries	0.0	0.0
Total stockholders' equity	2,239.6	3,192.0
Total liabilities and stockholders' equity	7,835.9	7,364.7
Non-Guarantor Subsidiaries [Member]
Current assets
Cash and cash equivalents	363.1	439.5
Accounts receivable, net	551.9	556.1
Intercompany receivables	122.6	93.5
Inventories, net	222.9	259.5
Other current assets	85.0	86.8
Total current assets	1,345.5	1,435.4
Property, plant and equipment, net	1,527.2	1,480.0
Goodwill	321.2	422.8
Other intangible assets, net	28.5	32.9
Intercompany notes and accounts receivable	0.0	0.0
Other assets and deferred charges	332.7	267.4
Investment in subsidiaries	0.0	0.0
Total assets	3,555.1	3,638.5
Current liabilities
Current portion of long-term debt	17.1	21.6
Accounts payable	395.6	499.5
Intercompany payables	64.6	121.3
Other current liabilities	184.4	190.2
Total current liabilities	661.7	832.6
Intercompany notes and accounts payable	566.6	144.6
Long-term debt, net	88.9	105.5
Other long-term liabilities	267.6	200.2
Total liabilities	1,584.8	1,282.9
Total AAM stockholders' equity	1,967.5	2,353.2
Noncontrolling interests in subsidiaries	2.8	2.4
Total stockholders' equity	1,970.3	2,355.6
Total liabilities and stockholders' equity	$ 3,555.1	$ 3,638.5