Segment, Major Customer and Major Supplier Information - Net Sales by Value Stream (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Segment Reporting Information [Line Items]
Net sales	$ 4,295	$ 4,107	$ 8,482	$ 8,198
Beverage packaging
Segment Reporting Information [Line Items]
Net sales	2,282	1,943	4,315	3,727
Automotive
Segment Reporting Information [Line Items]
Net sales	842	971	1,822	1,989
Aerospace and industrial plate
Segment Reporting Information [Line Items]
Net sales	186	179	346	355
Specialty
Segment Reporting Information [Line Items]
Net sales	$ 985	$ 1,014	$ 1,999	$ 2,127