Supplemental Guarantor Condensed Consolidating Financial Statements Supplemental Guarantor Condensed Consolidating Financial Statements Parenthetical (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Cost of goods sold	$ 810.1us-gaap_CostOfGoodsSold	$ 695.5us-gaap_CostOfGoodsSold	$ 2,344.9us-gaap_CostOfGoodsSold	$ 2,024.2us-gaap_CostOfGoodsSold
Income tax expense	7.5us-gaap_IncomeTaxExpenseBenefit	6.1us-gaap_IncomeTaxExpenseBenefit	25.8us-gaap_IncomeTaxExpenseBenefit	9.1us-gaap_IncomeTaxExpenseBenefit
Investment in subsidiaries	0us-gaap_EquityMethodInvestments		0us-gaap_EquityMethodInvestments		0us-gaap_EquityMethodInvestments
Other current assets	110.8us-gaap_OtherAssetsCurrent		110.8us-gaap_OtherAssetsCurrent		122.0us-gaap_OtherAssetsCurrent
Earnings (loss) from equity in subsidiaries	0	0	0	0
As previously reported
Cost of goods sold	801.7		2,336.5
Income tax expense	11.3		29.6
Adjustment
Cost of goods sold	8.4		8.4
Income tax expense	(3.8)		(3.8)
AAM Inc. [Member]
Cost of goods sold	291.9	170.1	812.3	566.3
Income tax expense	6.6	0.9	13.4	(13.0)
Investment in subsidiaries	1,401.4		1,401.4		1,240.1
Other current assets	39.9		39.9		43.8
Earnings (loss) from equity in subsidiaries	63.9	50.7	186.7	115.6
AAM Inc. [Member] \| As previously reported
Investment in subsidiaries	1,399.1		1,399.1
Earnings (loss) from equity in subsidiaries	68.5		191.3
AAM Inc. [Member] \| Adjustment
Investment in subsidiaries	2.3		2.3
Earnings (loss) from equity in subsidiaries	(4.6)		(4.6)
Holdings [Member]
Cost of goods sold	0	0	0	0
Income tax expense	0	0	0	0
Investment in subsidiaries	495.0		495.0		363.7
Other current assets	0		0		0
Earnings (loss) from equity in subsidiaries	44.0	31.6	129.8	64.7
Holdings [Member] \| As previously reported
Investment in subsidiaries	492.7		492.7
Earnings (loss) from equity in subsidiaries	48.6		134.4
Holdings [Member] \| Adjustment
Investment in subsidiaries	2.3		2.3
Earnings (loss) from equity in subsidiaries	(4.6)		(4.6)
Non-Guarantor Subsidiaries [Member]
Cost of goods sold	489.8	490.1	1,440.1	1,355.7
Income tax expense	0.8	5.2	12.1	22.1
Investment in subsidiaries	0		0		0
Other current assets	67.9		67.9		75.0
Earnings (loss) from equity in subsidiaries	0	0	0	0
Non-Guarantor Subsidiaries [Member] \| As previously reported
Cost of goods sold	481.4		1,431.7
Income tax expense	4.6		15.9
Other current assets	65.6		65.6
Non-Guarantor Subsidiaries [Member] \| Adjustment
Cost of goods sold	8.4		8.4
Income tax expense	(3.8)		(3.8)
Other current assets	$ 2.3		$ 2.3

Supplemental Guarantor Condensed Consolidating Financial Statements Supplemental Guarantor Condensed Consolidating Financial Statements Parenthetical (Details) (USD $)
In Millions, unless otherwise specified