Supplemental Guarantor Condensed Consolidating Statements of Cash Flows (Details) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Net cash provided by (used in) operating activities	$ 136.9	$ 289.4
Investing activities
Purchases of property, plant and equipment	(237.5)	(273.0)
Proceeds from sale of property, plant and equipment	1.7	0.9
Investment in joint venture	(2.2)	0.0
Purchase buyouts of leased equipment	0.0	(0.5)
Proceeds from sale of business, net	0.0	47.1
Acquisition of business	0.0	(1.3)
Intercompany Activity - Investing	0.0
Net cash used in investing activities	(238.0)	(226.8)
Financing activities
Net debt activity	(120.2)	(66.8)
Debt issuance costs	0.0	(6.8)
Purchase of treasury stock	(7.5)	(3.6)
Purchase of noncontrolling interest	0.0	(2.2)
Intercompany Activity - Financing	0.0	0.0
Net cash used in financing activities	(127.7)	(79.4)
Effect of exchange rate changes on cash	1.2	(4.3)
Net increase (decrease) in cash, cash equivalents and restricted cash	(227.6)	(21.1)
Cash, cash equivalents and restricted cash	251.3	355.7	$ 478.9	$ 376.8
Consolidation, Eliminations [Member]
Net cash provided by (used in) operating activities	0.0	0.0
Investing activities
Purchases of property, plant and equipment	0.0	0.0
Proceeds from sale of property, plant and equipment	0.0	0.0
Investment in joint venture	0.0
Purchase buyouts of leased equipment		0.0
Proceeds from sale of business, net		0.0
Acquisition of business		0.0
Intercompany Activity - Investing	0.0
Net cash used in investing activities	0.0	0.0
Financing activities
Net debt activity	0.0	0.0
Debt issuance costs		0.0
Purchase of treasury stock	0.0	0.0
Purchase of noncontrolling interest		0.0
Intercompany Activity - Financing	0.0	0.0
Net cash used in financing activities	0.0	0.0
Effect of exchange rate changes on cash	0.0	0.0
Net increase (decrease) in cash, cash equivalents and restricted cash	0.0	0.0
Cash, cash equivalents and restricted cash	0.0	0.0	0.0	0.0
Holdings [Member]
Net cash provided by (used in) operating activities	0.0	0.0
Investing activities
Purchases of property, plant and equipment	0.0	0.0
Proceeds from sale of property, plant and equipment	0.0	0.0
Investment in joint venture	0.0
Purchase buyouts of leased equipment		0.0
Proceeds from sale of business, net		0.0
Acquisition of business		0.0
Intercompany Activity - Investing	0.0
Net cash used in investing activities	0.0	0.0
Financing activities
Net debt activity	0.0	0.0
Debt issuance costs		0.0
Purchase of treasury stock	(7.5)	(3.6)
Purchase of noncontrolling interest		0.0
Intercompany Activity - Financing	7.5	3.6
Net cash used in financing activities	0.0	0.0
Effect of exchange rate changes on cash	0.0	0.0
Net increase (decrease) in cash, cash equivalents and restricted cash	0.0	0.0
Cash, cash equivalents and restricted cash	0.0	0.0	0.0	0.0
AAM Inc. [Member]
Net cash provided by (used in) operating activities	186.8	152.3
Investing activities
Purchases of property, plant and equipment	(32.8)	(40.3)
Proceeds from sale of property, plant and equipment	0.0	0.0
Investment in joint venture	0.0
Purchase buyouts of leased equipment		0.0
Proceeds from sale of business, net		0.0
Acquisition of business		0.0
Intercompany Activity - Investing	0.0
Net cash used in investing activities	(32.8)	(40.3)
Financing activities
Net debt activity	(112.0)	(111.2)
Debt issuance costs		(6.8)
Purchase of treasury stock	0.0	0.0
Purchase of noncontrolling interest		0.0
Intercompany Activity - Financing	(7.5)	(3.6)
Net cash used in financing activities	(119.5)	(121.6)
Effect of exchange rate changes on cash	0.0	0.0
Net increase (decrease) in cash, cash equivalents and restricted cash	34.5	(9.6)
Cash, cash equivalents and restricted cash	71.2	82.3	36.7	91.9
Guarantor Subsidiaries [Member]
Net cash provided by (used in) operating activities	65.2	8.6
Investing activities
Purchases of property, plant and equipment	(60.4)	(74.5)
Proceeds from sale of property, plant and equipment	1.7	0.5
Investment in joint venture	0.0
Purchase buyouts of leased equipment		(0.5)
Proceeds from sale of business, net		42.7
Acquisition of business		0.0
Intercompany Activity - Investing	(6.4)
Net cash used in investing activities	(65.1)	(31.8)
Financing activities
Net debt activity	(0.2)	(0.4)
Debt issuance costs		0.0
Purchase of treasury stock	0.0	0.0
Purchase of noncontrolling interest		(2.2)
Intercompany Activity - Financing	0.0	28.5
Net cash used in financing activities	(0.2)	25.9
Effect of exchange rate changes on cash	0.0	0.0
Net increase (decrease) in cash, cash equivalents and restricted cash	(0.1)	2.7
Cash, cash equivalents and restricted cash	2.6	2.8	2.7	0.1
Non-Guarantor Subsidiaries [Member]
Net cash provided by (used in) operating activities	(115.1)	128.5
Investing activities
Purchases of property, plant and equipment	(144.3)	(158.2)
Proceeds from sale of property, plant and equipment	0.0	0.4
Investment in joint venture	(2.2)
Purchase buyouts of leased equipment		0.0
Proceeds from sale of business, net		4.4
Acquisition of business		(1.3)
Intercompany Activity - Investing	6.4
Net cash used in investing activities	(140.1)	(154.7)
Financing activities
Net debt activity	(8.0)	44.8
Debt issuance costs		0.0
Purchase of treasury stock	0.0	0.0
Purchase of noncontrolling interest		0.0
Intercompany Activity - Financing	0.0	(28.5)
Net cash used in financing activities	(8.0)	16.3
Effect of exchange rate changes on cash	1.2	(4.3)
Net increase (decrease) in cash, cash equivalents and restricted cash	(262.0)	(14.2)
Cash, cash equivalents and restricted cash	$ 177.5	$ 270.6	$ 439.5	$ 284.8

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