Consolidated Statements of Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]	AOCI Attributable to Parent [Member]	Noncontrolling Interest [Member]
Common stock, shares, outstanding at Dec. 31, 2016	76.5
Total AAM stockholders' equity at Dec. 31, 2016		$ 0.9	$ 660.1	$ 423.9	$ (191.1)	$ (389.6)	$ 0.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to AAM	$ 337.1			337.1
Net income attributable to noncontrolling interests	$ (0.4)						0.4
Changes in cash flow hedges						17.1
Foreign currency translation adjustments						88.3
Defined benefit plans, net						(8.5)
Stock issued during period, shares, acquisitions	34.3
Acquisition of MPG	$ 576.7	0.3	579.6		(1.7)		3.6
Stock issued during period, shares, share-based compensation, net of forfeitures	0.8
Stock issued during period, value, share-based compensation, net of forfeitures			0.9
Stock-based compensation			24.0
Treasury stock, shares, acquired	(0.3)
Purchase of treasury stock	$ 7.0				(5.3)
Common stock, shares, outstanding at Dec. 31, 2017	111.3
Total AAM stockholders' equity at Dec. 31, 2017		1.2	1,264.6	761.0	(198.1)	(292.7)	4.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to AAM	$ (57.5)			(57.5)
Net income attributable to noncontrolling interests	(0.7)						0.7
Changes in cash flow hedges						5.5
Foreign currency translation adjustments						(62.5)
Defined benefit plans, net						38.1
Acquisition of MPG	$ 0.0
Purchase of noncontrolling interest							(2.3)
Stock issued during period, shares, share-based compensation, net of forfeitures	0.7
Stock issued during period, value, share-based compensation, net of forfeitures			0.1
Stock-based compensation			27.9
Treasury stock, shares, acquired	(0.3)
Purchase of treasury stock	$ 3.7				(3.7)
Common stock, shares, outstanding at Dec. 31, 2018	111.7
Total AAM stockholders' equity at Dec. 31, 2018	$ 1,483.9	1.2	1,292.6	703.5	(201.8)	(311.6)	2.4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to AAM	(484.5)			(484.5)
Net income attributable to noncontrolling interests	(0.4)						0.4
Changes in cash flow hedges						(14.6)
Foreign currency translation adjustments						(4.6)
Defined benefit plans, net						(18.3)
Acquisition of MPG	$ 0.0
Stock issued during period, shares, share-based compensation, net of forfeitures	1.3
Stock-based compensation			21.3
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification | ASU 2016-02 [Member]				1.9
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification | ASU 2018-02 [Member]				27.7		(27.7)
Treasury stock, shares, acquired	(0.4)
Purchase of treasury stock	$ 7.5				(7.5)
Common stock, shares, outstanding at Dec. 31, 2019	112.6
Total AAM stockholders' equity at Dec. 31, 2019	$ 977.6	$ 1.2	$ 1,313.9	$ 248.6	$ (209.3)	$ (376.8)	$ 2.8