Supplemental Guarantor Condensed Consolidating Financial Statements Supplemental Guarantor Condensed Consolidating Balance Sheets (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
Current assets
Cash and cash equivalents	$ 388.4	$ 282.5	$ 301.3	$ 249.2
Accounts receivable, net	641.7	539.1
Intercompany receivables	0.0	0.0
Inventories, net	226.9	230.5
Prepaid expenses and other	77.4	72.1
Total current assets	1,334.4	1,124.2
Property, plant and equipment, net	1,080.7	1,046.2
Goodwill	154.4	154.4
Intercompany notes and accounts receivable	0.0	0.0
Other assets and deferred charges	863.2	877.9
Investment in subsidiaries	0.0	0.0
Total assets	3,432.7	3,202.7
Current liabilities
Current portion of long-term debt	3.4	3.3
Accounts payable	503.8	412.7
Intercompany payables	0.0	0.0
Accrued expenses and other	244.7	283.2
Total current liabilities	751.9	699.2
Intercompany notes and accounts payable	0.0	0.0
Long-term debt, net	1,403.3	1,375.7
Investment in Subsidiaries Obligation	0.0	0.0
Other long-term liabilities	820.1	826.3
Total liabilities	2,975.3	2,901.2
Total stockholders’ equity	457.4	301.5
Total liabilities and stockholders' equity	3,432.7	3,202.7
Holdings [Member]
Current assets
Cash and cash equivalents	0.0	0.0	0.0	0.0
Accounts receivable, net	0.0	0.0
Intercompany receivables	0.0	0.0
Inventories, net	0.0	0.0
Prepaid expenses and other	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
Intercompany notes and accounts receivable	0.0	0.0
Other assets and deferred charges	0.0	0.0
Investment in subsidiaries	783.3	622.3
Total assets	783.3	622.3
Current liabilities
Current portion of long-term debt	0.0	0.0
Accounts payable	0.0	0.0
Intercompany payables	0.0	0.0
Accrued expenses and other	0.0	0.0
Total current liabilities	0.0	0.0
Intercompany notes and accounts payable	325.9	320.8
Long-term debt, net	0.0	0.0
Investment in Subsidiaries Obligation	0.0	0.0
Other long-term liabilities	0.0	0.0
Total liabilities	325.9	320.8
Total stockholders’ equity	457.4	301.5
Total liabilities and stockholders' equity	783.3	622.3
AAM Inc. [Member]
Current assets
Cash and cash equivalents	169.1	52.0	126.9	69.7
Accounts receivable, net	159.2	127.2
Intercompany receivables	296.5	311.8
Inventories, net	53.7	59.8
Prepaid expenses and other	24.1	30.4
Total current assets	702.6	581.2
Property, plant and equipment, net	213.0	214.1
Goodwill	0.0	0.0
Intercompany notes and accounts receivable	346.9	393.5
Other assets and deferred charges	653.8	683.6
Investment in subsidiaries	1,487.6	1,315.9
Total assets	3,403.9	3,188.3
Current liabilities
Current portion of long-term debt	0.0	0.0
Accounts payable	146.6	103.0
Intercompany payables	293.9	248.7
Accrued expenses and other	123.0	134.2
Total current liabilities	563.5	485.9
Intercompany notes and accounts payable	0.0	10.3
Long-term debt, net	1,337.8	1,336.5
Investment in Subsidiaries Obligation	0.0	0.0
Other long-term liabilities	719.3	733.3
Total liabilities	2,620.6	2,566.0
Total stockholders’ equity	783.3	622.3
Total liabilities and stockholders' equity	3,403.9	3,188.3
Guarantor Subsidiaries [Member]
Current assets
Cash and cash equivalents	0.0	0.0	0.0	0.0
Accounts receivable, net	28.2	19.7
Intercompany receivables	297.0	249.7
Inventories, net	28.0	31.1
Prepaid expenses and other	0.4	0.5
Total current assets	353.6	301.0
Property, plant and equipment, net	95.4	91.9
Goodwill	147.8	147.8
Intercompany notes and accounts receivable	248.7	252.2
Other assets and deferred charges	42.1	41.4
Investment in subsidiaries	0.0	0.0
Total assets	887.6	834.3
Current liabilities
Current portion of long-term debt	0.0	0.0
Accounts payable	43.5	35.8
Intercompany payables	160.3	154.9
Accrued expenses and other	4.7	4.1
Total current liabilities	208.5	194.8
Intercompany notes and accounts payable	26.1	0.0
Long-term debt, net	4.3	4.5
Investment in Subsidiaries Obligation	105.9	111.7
Other long-term liabilities	0.5	0.5
Total liabilities	345.3	311.5
Total stockholders’ equity	542.3	522.8
Total liabilities and stockholders' equity	887.6	834.3
Non-Guarantor Subsidiaries [Member]
Current assets
Cash and cash equivalents	219.3	230.5	174.4	179.5
Accounts receivable, net	454.3	392.2
Intercompany receivables	9.1	9.4
Inventories, net	145.2	139.6
Prepaid expenses and other	52.9	41.2
Total current assets	880.8	812.9
Property, plant and equipment, net	772.3	740.2
Goodwill	6.6	6.6
Intercompany notes and accounts receivable	0.0	0.0
Other assets and deferred charges	167.3	152.9
Investment in subsidiaries	0.0	0.0
Total assets	1,827.0	1,712.6
Current liabilities
Current portion of long-term debt	3.4	3.3
Accounts payable	313.7	273.9
Intercompany payables	148.4	167.3
Accrued expenses and other	117.0	144.9
Total current liabilities	582.5	589.4
Intercompany notes and accounts payable	243.6	314.6
Long-term debt, net	61.2	34.7
Investment in Subsidiaries Obligation	0.0	0.0
Other long-term liabilities	100.3	92.5
Total liabilities	987.6	1,031.2
Total stockholders’ equity	839.4	681.4
Total liabilities and stockholders' equity	1,827.0	1,712.6
Consolidation, Eliminations [Member]
Current assets
Cash and cash equivalents	0.0	0.0	$ 0.0	$ 0.0
Accounts receivable, net	0.0	0.0
Intercompany receivables	(602.6)	(570.9)
Inventories, net	0.0	0.0
Prepaid expenses and other	0.0	0.0
Total current assets	(602.6)	(570.9)
Property, plant and equipment, net	0.0	0.0
Goodwill	0.0	0.0
Intercompany notes and accounts receivable	(595.6)	(645.7)
Other assets and deferred charges	0.0	0.0
Investment in subsidiaries	(2,270.9)	(1,938.2)
Total assets	(3,469.1)	(3,154.8)
Current liabilities
Current portion of long-term debt	0.0	0.0
Accounts payable	0.0	0.0
Intercompany payables	(602.6)	(570.9)
Accrued expenses and other	0.0	0.0
Total current liabilities	(602.6)	(570.9)
Intercompany notes and accounts payable	(595.6)	(645.7)
Long-term debt, net	0.0	0.0
Investment in Subsidiaries Obligation	(105.9)	(111.7)
Other long-term liabilities	0.0	0.0
Total liabilities	(1,304.1)	(1,328.3)
Total stockholders’ equity	(2,165.0)	(1,826.5)
Total liabilities and stockholders' equity	$ (3,469.1)	$ (3,154.8)