Receivables (Details) - USD ($)		3 Months Ended		12 Months Ended
	Mar. 30, 2012	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Schedule Of Financial Receivables [Line Items]
Funding of customer receivables sold, maximum		$ 52,000,000
Deferred purchase program receivable	$ 254,000,000	65,000,000		$ 246,000,000
Sale of customer receivables	304,000,000
Cash received for receivables	$ 50,000,000	48,000,000	$ 160,000,000
Net cash funding received during the period		248,000,000
Amount of cash draws under arrangement during the period		3,656,000,000
Amount of cash repayments under arrangement during the period		(3,408,000,000)
Amount of cash repayments under arrangement since inception		(150,000,000)
Amount of cash draws under arrangement since inception		98,000,000
Accounts receivables sold		31,000,000
Global Rolled Products
Schedule Of Financial Receivables [Line Items]
Deferred purchase program receivable		282,000,000
Maximum
Schedule Of Financial Receivables [Line Items]
Funding of customer receivables sold, maximum		$ 300,000,000		$ 400,000,000