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Earnings Per Share (Details) (USD $)
In Millions, except Per Share data, unless otherwise specified
 3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Mar. 31, 2011
Jun. 30, 2012
Jun. 30, 2011
Dec. 31, 2009
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]            
Net income attributable to AAM $ 4.7 $ 49.2   $ 55.9 $ 86.9  
Weighted average number of shares outstanding, basic 75.1 75.4   75.1 74.5  
Dilutive securities, effect on basic earnings per share, including Options and Restrictive Stock Units 0 0   0 0.2  
Dilutive securities, effect on basic earnings per share $ 0 $ 0   $ 0 $ 0.7  
Weighted average number of shares outstanding, diluted 75.1 75.4   75.1 75.4  
Basic earnings per share $ 0.06 $ 0.65   $ 0.74 $ 1.17  
Diluted earnings per share $ 0.06 $ 0.65   $ 0.74 $ 1.15  
Earnings per share, Stock Options excluded from the calculation of diluted EPS 3.3 4.1   3.3 4.1  
Earnings per share, range of exercise prices of Stock Options excluded from the calculation of diluted EPS, lower end of range $ 15.58 $ 15.56   $ 15.58 $ 15.56  
Earnings per share, range of exercise prices of Stock Options excluded from the calculation of diluted EPS, upper end of range $ 40.83 $ 40.83   $ 40.83 $ 40.83  
2009 GM Agreement, number of shares available for purchase through exercise of warrants           4.1
2009 GM Agreement, exercise price of warrants issued to GM           $ 2.76
2009 GM Agreement, shares issued to GM through exercise of warrants     3.3