Business Combinations - Business Combinations (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Apr. 06, 2017	Mar. 01, 2017
Business Acquisition [Line Items]
Adjusted purchase price, net of cash acquired			$ 9.4	$ 1.3	$ 895.5
Goodwill			$ 699.1	$ 1,141.8	1,654.3
Metaldyne Performance Group, Inc. [Member]
Business Acquisition [Line Items]
Cash consideration	$ 953.5
Adjustment to Contractual Purchase Price - Existing Payable Balance						$ (12.4)
Share consideration	576.7
Total consideration transferred	$ 1,530.2				$ 1,500.0
Fair value of MPG noncontrolling interests						3.6
Total fair value of MPG						1,533.8
Cash and cash equivalents acquired						(202.1)
Accounts receivable						403.1
Inventories						199.0
Prepaid expenses and other long-term assets						119.9
Property, plant and equipment						971.8
Intangible assets						1,223.1
Total assets acquired						3,119.0
Accounts payable						287.8
Accrued expenses and other						137.7
Deferred income tax liabilities						580.2
Debt						1,918.7
Postretirement benefits and other long-term liabilities						54.1
Net assets acquired						140.5
Goodwill						$ 1,393.3
Percentage of equity interests acquired						100.00%
USM Mexico Manufacturing LLC [Member]
Business Acquisition [Line Items]
Cash consideration		$ 162.5
Adjustments to Contractual Purchase Price for Working Capital Settlement							$ 2.5
Adjustments to Contractual Purchase Price for Capital Equipment							4.9
Adjustment to Contractual Purchase Price - Existing Payable Balance							(22.8)
Cash and cash equivalents acquired							(0.5)
Accounts receivable							1.1
Inventories							4.8
Prepaid expenses and other long-term assets							3.6
Property, plant and equipment							38.4
Intangible assets							31.7
Total assets acquired							79.6
Accounts payable							10.8
Accrued expenses and other							2.7
Deferred income tax liabilities							1.2
Adjusted purchase price, net of cash acquired		$ 146.6
Net assets acquired							64.9
Goodwill							$ 81.7
Percentage of equity interests acquired							100.00%