Supplemental Guarantor Condensed Consolidating Financial Statements - Condensed Consolidating Statements of Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net sales
External	$ 6,530.9	$ 7,270.4	$ 6,266.0
Intercompany	0.0	0.0	0.0
Total net sales	6,530.9	7,270.4	6,266.0
Cost of goods sold	5,628.3	6,130.0	5,146.9
Gross profit	902.6	1,140.4	1,119.1
Selling, general and administrative expenses	364.7	385.7	390.1
Amortization of intangible assets	95.4	99.4	75.3
Impairment charges	665.0	485.5	0.0
Restructuring and acquisition-related costs	57.8	78.9	110.7
(Gain) loss on sale of business	21.3	(15.5)	0.0
Operating income (loss)	(301.6)	106.4	543.0
Non-operating income (expense), net	(231.4)	(220.3)	(203.0)
Income (loss) before income taxes	(533.0)	(113.9)	340.0
Income tax expense (benefit)	(48.9)	(57.1)	2.5
Earnings (loss) from equity in subsidiaries	0.0	0.0	0.0
Net income (loss) before royalties	(484.1)	(56.8)	337.5
Royalties	0.0	0.0	0.0
Net income (loss) after royalties	(484.1)	(56.8)	337.5
Net income attributable to noncontrolling interests	(0.4)	(0.7)	(0.4)
Net income (loss) attributable to AAM	(484.5)	(57.5)	337.1
Other comprehensive income (loss), net of tax	(37.5)	(18.9)	96.9
Comprehensive income (loss)	(522.0)	(76.4)	434.0
Consolidation, Eliminations [Member]
Net sales
External	0.0	0.0	0.0
Intercompany	(324.3)	(340.9)	(315.1)
Total net sales	(324.3)	(340.9)	(315.1)
Cost of goods sold	(324.3)	(340.9)	(315.1)
Gross profit	0.0	0.0	0.0
Selling, general and administrative expenses	0.0	0.0	0.0
Amortization of intangible assets	0.0	0.0	0.0
Impairment charges	0.0	0.0
Restructuring and acquisition-related costs	0.0	0.0	0.0
(Gain) loss on sale of business	0.0	0.0
Operating income (loss)	0.0	0.0	0.0
Non-operating income (expense), net	0.0	0.0	0.0
Income (loss) before income taxes	0.0	0.0	0.0
Income tax expense (benefit)	0.0	0.0	0.0
Earnings (loss) from equity in subsidiaries	688.3	57.8	(702.7)
Net income (loss) before royalties	688.3	57.8	(702.7)
Royalties	0.0	0.0	0.0
Net income (loss) after royalties	688.3	57.8	(702.7)
Net income attributable to noncontrolling interests	0.0	0.0	0.0
Net income (loss) attributable to AAM	688.3	57.8	(702.7)
Other comprehensive income (loss), net of tax	58.7	86.4	(230.0)
Comprehensive income (loss)	747.0	144.2	(932.7)
Holdings [Member]
Net sales
External	0.0	0.0	0.0
Intercompany	0.0	0.0	0.0
Total net sales	0.0	0.0	0.0
Cost of goods sold	0.0	0.0	0.0
Gross profit	0.0	0.0	0.0
Selling, general and administrative expenses	0.0	0.0	0.0
Amortization of intangible assets	0.0	0.0	0.0
Impairment charges	0.0	0.0
Restructuring and acquisition-related costs	0.0	0.0	0.0
(Gain) loss on sale of business	0.0	0.0
Operating income (loss)	0.0	0.0	0.0
Non-operating income (expense), net	0.0	0.0	0.0
Income (loss) before income taxes	0.0	0.0	0.0
Income tax expense (benefit)	0.0	0.0	0.0
Earnings (loss) from equity in subsidiaries	(484.5)	(57.5)	337.1
Net income (loss) before royalties	(484.5)	(57.5)	337.1
Royalties	0.0	0.0	0.0
Net income (loss) after royalties	(484.5)	(57.5)	337.1
Net income attributable to noncontrolling interests	0.0	0.0	0.0
Net income (loss) attributable to AAM	(484.5)	(57.5)	337.1
Other comprehensive income (loss), net of tax	(37.5)	(18.9)	96.9
Comprehensive income (loss)	(522.0)	(76.4)	434.0
AAM Inc. [Member]
Net sales
External	902.0	1,088.4	1,074.6
Intercompany	1.9	4.2	2.4
Total net sales	903.9	1,092.6	1,077.0
Cost of goods sold	913.2	1,033.8	996.6
Gross profit	(9.3)	58.8	80.4
Selling, general and administrative expenses	232.5	210.3	223.2
Amortization of intangible assets	5.9	5.1	5.6
Impairment charges	0.0	0.0
Restructuring and acquisition-related costs	24.3	34.2	105.2
(Gain) loss on sale of business	0.0	0.0
Operating income (loss)	(272.0)	(190.8)	(253.6)
Non-operating income (expense), net	(247.0)	(260.6)	(210.0)
Income (loss) before income taxes	(519.0)	(451.4)	(463.6)
Income tax expense (benefit)	(76.5)	(34.2)	194.1
Earnings (loss) from equity in subsidiaries	(218.3)	(168.3)	289.5
Net income (loss) before royalties	(660.8)	(585.5)	(368.2)
Royalties	224.4	276.6	317.3
Net income (loss) after royalties	(436.4)	(308.9)	(50.9)
Net income attributable to noncontrolling interests	0.0	0.0	0.0
Net income (loss) attributable to AAM	(436.4)	(308.9)	(50.9)
Other comprehensive income (loss), net of tax	(28.3)	9.4	40.1
Comprehensive income (loss)	(464.7)	(299.5)	(10.8)
Guarantor Subsidiaries [Member]
Net sales
External	1,992.0	2,204.8	1,668.2
Intercompany	274.7	294.8	285.2
Total net sales	2,266.7	2,499.6	1,953.4
Cost of goods sold	2,065.4	2,249.0	1,730.9
Gross profit	201.3	250.6	222.5
Selling, general and administrative expenses	27.7	81.4	63.9
Amortization of intangible assets	85.8	90.8	67.5
Impairment charges	566.1	485.5
Restructuring and acquisition-related costs	21.7	40.4	1.9
(Gain) loss on sale of business	21.3	(15.5)
Operating income (loss)	(521.3)	(432.0)	89.2
Non-operating income (expense), net	7.7	15.6	18.6
Income (loss) before income taxes	(513.6)	(416.4)	107.8
Income tax expense (benefit)	(10.7)	(55.4)	(247.0)
Earnings (loss) from equity in subsidiaries	14.5	168.0	76.1
Net income (loss) before royalties	(488.4)	(193.0)	430.9
Royalties	3.0	3.4	3.6
Net income (loss) after royalties	(485.4)	(189.6)	434.5
Net income attributable to noncontrolling interests	0.0	0.0	0.0
Net income (loss) attributable to AAM	(485.4)	(189.6)	434.5
Other comprehensive income (loss), net of tax	(18.3)	(51.6)	87.3
Comprehensive income (loss)	(503.7)	(241.2)	521.8
Non-Guarantor Subsidiaries [Member]
Net sales
External	3,636.9	3,977.2	3,523.2
Intercompany	47.7	41.9	27.5
Total net sales	3,684.6	4,019.1	3,550.7
Cost of goods sold	2,974.0	3,188.1	2,734.5
Gross profit	710.6	831.0	816.2
Selling, general and administrative expenses	104.5	94.0	103.0
Amortization of intangible assets	3.7	3.5	2.2
Impairment charges	98.9	0.0
Restructuring and acquisition-related costs	11.8	4.3	3.6
(Gain) loss on sale of business	0.0	0.0
Operating income (loss)	491.7	729.2	707.4
Non-operating income (expense), net	7.9	24.7	(11.6)
Income (loss) before income taxes	499.6	753.9	695.8
Income tax expense (benefit)	38.3	32.5	55.4
Earnings (loss) from equity in subsidiaries	0.0	0.0	0.0
Net income (loss) before royalties	461.3	721.4	640.4
Royalties	(227.4)	(280.0)	(320.9)
Net income (loss) after royalties	233.9	441.4	319.5
Net income attributable to noncontrolling interests	(0.4)	(0.7)	(0.4)
Net income (loss) attributable to AAM	233.5	440.7	319.1
Other comprehensive income (loss), net of tax	(12.1)	(44.2)	102.6
Comprehensive income (loss)	$ 221.4	$ 396.5	$ 421.7