Supplemental Guarantor Condensed Consolidating Statements of Operations (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Net sales
External	$ 1,677.4	$ 1,817.0	$ 5,100.9	$ 5,576.3
Intercompany	0.0	0.0	0.0	0.0
Net sales	1,677.4	1,817.0	5,100.9	5,576.3
Cost of goods sold	1,428.7	1,549.6	4,381.7	4,661.2
Gross profit	248.7	267.4	719.2	915.1
Selling, general and administrative expenses	92.7	96.3	274.7	288.6
Amortization of intangible assets	23.7	24.8	73.6	74.5
Impairment charge	225.0	0.0	225.0	0.0
Restructuring and acquisition-related costs	11.7	11.7	36.0	66.8
Gain on sale of business	0.0	0.0	0.0	(15.5)
Operating income (loss)	(104.4)	134.6	109.9	500.7
Non-operating income (expense), net	(60.1)	(59.1)	(177.0)	(164.5)
Income (loss) before income taxes	(164.5)	75.5	(67.1)	336.2
Income tax expense (benefit)	(40.4)	11.5	(37.4)	31.4
Earnings (loss) from equity in subsidiaries	0.0	0.0	0.0	0.0
Net income (loss) before royalties	(124.1)	64.0	(29.7)	304.8
Royalties	0.0	0.0	0.0	0.0
Net income (loss) after royalties	(124.1)	64.0	(29.7)	304.8
Net income attributable to noncontrolling interests	(0.1)	(0.2)	(0.4)	(0.5)
Net income (loss) attributable to AAM	(124.2)	63.8	(30.1)	304.3
Other comprehensive income (loss), net of tax	(44.8)	1.5	(58.9)	(20.9)
Comprehensive income (loss) attributable to AAM	(169.0)	65.3	(89.0)	283.4
Consolidation, Eliminations [Member]
Net sales
External	0.0	0.0	0.0	0.0
Intercompany	(94.0)	(87.1)	(258.5)	(266.7)
Net sales	(94.0)	(87.1)	(258.5)	(266.7)
Cost of goods sold	(94.0)	(87.1)	(258.5)	(266.7)
Gross profit	0.0	0.0	0.0	0.0
Selling, general and administrative expenses	0.0	0.0	0.0	0.0
Amortization of intangible assets	0.0	0.0	0.0	0.0
Impairment charge	0.0		0.0
Restructuring and acquisition-related costs	0.0	0.0	0.0	0.0
Gain on sale of business				0.0
Operating income (loss)	0.0	0.0	0.0	0.0
Non-operating income (expense), net	0.0	0.0	0.0	0.0
Income (loss) before income taxes	0.0	0.0	0.0	0.0
Income tax expense (benefit)	0.0	0.0	0.0	0.0
Earnings (loss) from equity in subsidiaries	35.5	(165.7)	(207.1)	(687.5)
Net income (loss) before royalties	35.5	(165.7)	(207.1)	(687.5)
Royalties	0.0	0.0	0.0	0.0
Net income (loss) after royalties	35.5	(165.7)	(207.1)	(687.5)
Net income attributable to noncontrolling interests	0.0	0.0	0.0	0.0
Net income (loss) attributable to AAM	35.5	(165.7)	(207.1)	(687.5)
Other comprehensive income (loss), net of tax	98.2	9.3	101.8	90.4
Comprehensive income (loss) attributable to AAM	133.7	(156.4)	(105.3)	(597.1)
Holdings [Member]
Net sales
External	0.0	0.0	0.0	0.0
Intercompany	0.0	0.0	0.0	0.0
Net sales	0.0	0.0	0.0	0.0
Cost of goods sold	0.0	0.0	0.0	0.0
Gross profit	0.0	0.0	0.0	0.0
Selling, general and administrative expenses	0.0	0.0	0.0	0.0
Amortization of intangible assets	0.0	0.0	0.0	0.0
Impairment charge	0.0		0.0
Restructuring and acquisition-related costs	0.0	0.0	0.0	0.0
Gain on sale of business				0.0
Operating income (loss)	0.0	0.0	0.0	0.0
Non-operating income (expense), net	0.0	0.0	0.0	0.0
Income (loss) before income taxes	0.0	0.0	0.0	0.0
Income tax expense (benefit)	0.0	0.0	0.0	0.0
Earnings (loss) from equity in subsidiaries	(124.2)	63.8	(30.1)	304.3
Net income (loss) before royalties	(124.2)	63.8	(30.1)	304.3
Royalties	0.0	0.0	0.0	0.0
Net income (loss) after royalties	(124.2)	63.8	(30.1)	304.3
Net income attributable to noncontrolling interests	0.0	0.0	0.0	0.0
Net income (loss) attributable to AAM	(124.2)	63.8	(30.1)	304.3
Other comprehensive income (loss), net of tax	(44.8)	1.5	(58.9)	(20.9)
Comprehensive income (loss) attributable to AAM	(169.0)	65.3	(89.0)	283.4
AAM Inc. [Member]
Net sales
External	205.7	247.1	711.8	851.4
Intercompany	0.5	0.7	1.5	4.0
Net sales	206.2	247.8	713.3	855.4
Cost of goods sold	221.2	220.6	721.1	804.5
Gross profit	(15.0)	27.2	(7.8)	50.9
Selling, general and administrative expenses	68.9	63.4	208.9	183.4
Amortization of intangible assets	1.4	1.0	4.3	3.9
Impairment charge	0.0		0.0
Restructuring and acquisition-related costs	6.2	5.0	17.1	31.1
Gain on sale of business				0.0
Operating income (loss)	(91.5)	(42.2)	(238.1)	(167.5)
Non-operating income (expense), net	(62.7)	(60.0)	(184.0)	(193.8)
Income (loss) before income taxes	(154.2)	(102.2)	(422.1)	(361.3)
Income tax expense (benefit)	(8.5)	(1.0)	(23.2)	8.1
Earnings (loss) from equity in subsidiaries	50.5	68.1	131.9	241.6
Net income (loss) before royalties	(95.2)	(33.1)	(267.0)	(127.8)
Royalties	86.6	87.6	241.2	256.8
Net income (loss) after royalties	(8.6)	54.5	(25.8)	129.0
Net income attributable to noncontrolling interests	0.0	0.0	0.0	0.0
Net income (loss) attributable to AAM	(8.6)	54.5	(25.8)	129.0
Other comprehensive income (loss), net of tax	(26.4)	1.0	(40.2)	(2.6)
Comprehensive income (loss) attributable to AAM	(35.0)	55.5	(66.0)	126.4
Guarantor Subsidiaries [Member]
Net sales
External	506.5	544.3	1,561.8	1,699.2
Intercompany	77.0	75.6	219.8	231.6
Net sales	583.5	619.9	1,781.6	1,930.8
Cost of goods sold	529.6	594.2	1,612.2	1,713.3
Gross profit	53.9	25.7	169.4	217.5
Selling, general and administrative expenses	6.8	19.6	22.4	61.4
Amortization of intangible assets	21.4	22.9	66.6	68.0
Impairment charge	225.0		225.0
Restructuring and acquisition-related costs	4.1	3.9	12.3	31.8
Gain on sale of business				(15.5)
Operating income (loss)	(203.4)	(20.7)	(156.9)	71.8
Non-operating income (expense), net	2.3	2.8	7.0	11.0
Income (loss) before income taxes	(201.1)	(17.9)	(149.9)	82.8
Income tax expense (benefit)	(46.8)	0.1	(46.7)	0.6
Earnings (loss) from equity in subsidiaries	38.2	33.8	105.3	141.6
Net income (loss) before royalties	(116.1)	15.8	2.1	223.8
Royalties	0.7	0.7	2.2	2.6
Net income (loss) after royalties	(115.4)	16.5	4.3	226.4
Net income attributable to noncontrolling interests	0.0	0.0	0.0	0.0
Net income (loss) attributable to AAM	(115.4)	16.5	4.3	226.4
Other comprehensive income (loss), net of tax	(35.4)	(10.3)	(32.1)	(50.5)
Comprehensive income (loss) attributable to AAM	(150.8)	6.2	(27.8)	175.9
Non-Guarantor Subsidiaries [Member]
Net sales
External	965.2	1,025.6	2,827.3	3,025.7
Intercompany	16.5	10.8	37.2	31.1
Net sales	981.7	1,036.4	2,864.5	3,056.8
Cost of goods sold	771.9	821.9	2,306.9	2,410.1
Gross profit	209.8	214.5	557.6	646.7
Selling, general and administrative expenses	17.0	13.3	43.4	43.8
Amortization of intangible assets	0.9	0.9	2.7	2.6
Impairment charge	0.0		0.0
Restructuring and acquisition-related costs	1.4	2.8	6.6	3.9
Gain on sale of business				0.0
Operating income (loss)	190.5	197.5	504.9	596.4
Non-operating income (expense), net	0.3	(1.9)	0.0	18.3
Income (loss) before income taxes	190.8	195.6	504.9	614.7
Income tax expense (benefit)	14.9	12.4	32.5	22.7
Earnings (loss) from equity in subsidiaries	0.0	0.0	0.0	0.0
Net income (loss) before royalties	175.9	183.2	472.4	592.0
Royalties	(87.3)	(88.3)	(243.4)	(259.4)
Net income (loss) after royalties	88.6	94.9	229.0	332.6
Net income attributable to noncontrolling interests	(0.1)	(0.2)	(0.4)	(0.5)
Net income (loss) attributable to AAM	88.5	94.7	228.6	332.1
Other comprehensive income (loss), net of tax	(36.4)	0.0	(29.5)	(37.3)
Comprehensive income (loss) attributable to AAM	$ 52.1	$ 94.7	$ 199.1	$ 294.8