Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]
Net income (loss)	$ (484.1)	$ (56.8)	$ 337.5
Depreciation and amortization	536.9	528.8	428.5
Impairment charges	667.9	515.5	1.5
Deferred income taxes	(94.6)	(35.0)	(154.2)
Stock-based compensation	22.4	27.9	43.4
Pensions and other postretirement benefits, net of contributions	(8.8)	(9.9)	(6.0)
(Gain) loss on sale or acquisition of business	10.5	(15.5)	0.0
(Gain) loss on disposal of property, plant and equipment, net	4.1	(3.2)	1.6
Debt refinancing and redemption costs and (gain) on settlement of capital lease	8.4	4.0	3.5
Changes in operating assets and liabilities, net of amounts acquired or disposed
Accounts receivable	63.9	56.1	(44.9)
Inventories	56.1	(83.1)	2.5
Accounts payable and accrued expenses	(97.7)	7.5	(12.6)
Deferred revenue	(17.9)	10.7	14.8
Other assets and liabilities	(107.5)	(175.5)	31.4
Net cash provided by operating activities	559.6	771.5	647.0
Investing activities
Purchases of property, plant and equipment	(433.3)	(524.7)	(477.7)
Proceeds from sale of property, plant and equipment	5.0	4.9	2.5
Purchase buyouts of leased equipment	(0.9)	(0.5)	(13.3)
Proceeds from sale of business, net	141.2	47.1	5.9
Acquisition of business, net of cash acquired	(9.4)	(1.3)	(895.5)
Investment in affiliates	(9.2)	(3.7)	0.0
Net cash used in investing activities	(306.6)	(478.2)	(1,378.1)
Financing activities
Net short-term proceeds from credit facilities	0.0	0.0	4.4
Proceeds from issuance of long-term debt	356.3	509.6	2,862.7
Payments of long-term debt, finance lease obligations and other	(545.5)	(681.2)	(2,154.4)
Debt issuance costs	(3.3)	(6.9)	(91.0)
Purchase of noncontrolling interest	0.0	(2.3)	0.0
Employee stock option exercises	0.0	0.0	0.9
Purchase of treasury stock	(7.5)	(3.7)	(7.0)
Net cash provided by (used in) financing activities	(200.0)	(184.5)	615.6
Effect of exchange rate changes on cash	0.1	(6.7)	11.1
Net increase (decrease) in cash, cash equivalents and restricted cash	53.1	102.1	(104.4)
Cash, cash equivalents and restricted cash at beginning of year	478.9	376.8	481.2
Cash, cash equivalents and restricted cash at end of year	532.0	478.9	376.8
Supplemental cash flow information
Interest paid	205.4	199.7	182.7
Income taxes paid, net	57.1	46.0	31.9
Non-cash investing activities: AAM common shares issued for acquisition of MPG	0.0	0.0	576.7
Twelve year deferred payment obligation at 6% [Member]
Supplemental cash flow information
Non-cash investing activities: Debt security received for sale of U.S. Casting	$ 60.0	$ 0.0	$ 0.0