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Unaudited Quarterly Financial Data (Details) - USD ($)
$ / shares in Units, $ in Millions
 3 Months Ended 12 Months Ended
Dec. 31, 2019
Sep. 30, 2019
Jun. 30, 2019
Mar. 31, 2019
Dec. 31, 2018
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Revenue from Contract with Customer, Excluding Assessed Tax                 $ 6,530.9 $ 7,270.4 $ 6,266.0
Gross profit                 902.6 1,140.4 1,119.1
Net Income (loss)                 (484.1) (56.8) 337.5
Net income (loss) attributable to AAM                 $ (484.5) $ (57.5) $ 337.1
Basic earnings (loss) per share                 $ (4.31) $ (0.51) $ 3.22
Diluted earnings (loss) per share                 $ (4.31) $ (0.51) $ 3.21
Impairment of long-lived assets to be disposed of, net of tax   $ 178.0                  
Goodwill, Impairment Loss                 $ 440.0 $ 485.5  
Gain (Loss) on disposition of business, net of tax $ 17.0                    
Gain on bargain purchase of business                 10.8 0.0 $ 0.0
Defined benefit plan, net periodic benefit cost (credit), gain (loss) due to settlement or curtailment, net of tax 8.0                    
Quarterly Information [Member]                      
Revenue from Contract with Customer, Excluding Assessed Tax 1,430.0 1,677.4 $ 1,704.3 $ 1,719.2 $ 1,694.1 $ 1,817.0 $ 1,900.9 $ 1,858.4      
Gross profit 183.4 248.7 248.3 222.2 225.3 267.4 331.4 316.3      
Net Income (loss) (454.4) (124.1) 52.7 41.7 (361.6) 64.0 151.3 89.5      
Net income (loss) attributable to AAM $ (454.4) $ (124.2) $ 52.5 $ 41.6 $ (361.8) $ 63.8 $ 151.1 $ 89.4      
Basic earnings (loss) per share $ (4.04) $ (1.10) $ 0.45 $ 0.36 $ (3.24) $ 0.55 $ 1.31 $ 0.78      
Diluted earnings (loss) per share $ (4.04) $ (1.10) $ 0.45 $ 0.36 $ (3.24) $ 0.55 $ 1.30 $ 0.78      
Metal Forming [Member]                      
Revenue from Contract with Customer, Excluding Assessed Tax                 1,453.5 1,617.7 $ 1,217.2
Goodwill, Impairment Loss $ 440.0               $ 440.0 $ 0.0  
Powertrain and Casting [Member]                      
Goodwill, Impairment Loss, Net of Tax         $ 400.0