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Earnings Per Share Earnings Per Share (Details) (USD $)
In Millions, except Per Share data, unless otherwise specified
 3 Months Ended 12 Months Ended
Dec. 31, 2013
Sep. 30, 2013
Jun. 30, 2013
Mar. 31, 2013
Dec. 31, 2012
Sep. 30, 2012
Jun. 30, 2012
Mar. 31, 2012
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]                      
Net income attributable to AAM $ 29.8 $ 31.6 $ 25.8 $ 7.3 $ 319.9 $ (8.1) $ 4.7 $ 51.2 $ 94.5 $ 367.7 $ 142.8
Basic shares outstanding - weighted average shares outstanding                 76.7 75.3 74.9
Effect of dilutive securities - dilutive stock options                 0.1 0.1 0.1
Effect of dilutive securities - dilutive warrants                 0 0 0.4
Diluted shares outstanding - adjusted weighted-average shares after assumed conversions                 76.8 75.4 75.4
Basic earnings per share $ 0.39 $ 0.41 $ 0.34 $ 0.10 $ 4.21 $ (0.11) $ 0.06 $ 0.68 $ 1.23 $ 4.88 $ 1.91
Diluted earnings per share $ 0.39 $ 0.41 $ 0.34 $ 0.10 $ 4.21 $ (0.11) $ 0.06 $ 0.68 $ 1.23 $ 4.87 $ 1.89
Retained Earnings [Member]
                      
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]                      
Net income attributable to AAM                 $ 94.5 $ 367.7 $ 142.8