Accumulated Other Comprehensive Income (Loss) AOCI Reclassifications Impact (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Jun. 30, 2014		Jun. 30, 2013
AOCI Reclassification [Line Items]
Income tax provision	$ (24)		$ (3)
Net income	35		14
Cash flow hedges [Member]
AOCI Reclassification [Line Items]
Amount of gain (loss) reclassified from AOCI into income/(expense) (effective portion)	0		22
Income tax provision	0		(7)
Net income	0		15
Cash flow hedges [Member] | Electricity contracts [Member] | Other expense (income), net [Member]
AOCI Reclassification [Line Items]
Amount of gain (loss) reclassified from AOCI into income/(expense) (effective portion)	(1)	[1]	(1)	[1]
Cash flow hedges [Member] | Electricity contracts [Member] | Cost of goods sold [Member]
AOCI Reclassification [Line Items]
Amount of gain (loss) reclassified from AOCI into income/(expense) (effective portion)	1	[2],[3]	0	[2],[3]
Cash flow hedges [Member] | Aluminium contracts [Member] | Cost of goods sold [Member]
AOCI Reclassification [Line Items]
Amount of gain (loss) reclassified from AOCI into income/(expense) (effective portion)	(6)	[2]	21	[2]
Cash flow hedges [Member] | Aluminium contracts [Member] | Net sales [Member]
AOCI Reclassification [Line Items]
Amount of gain (loss) reclassified from AOCI into income/(expense) (effective portion)	0		2
Cash flow hedges [Member] | Currency exchange contracts [Member] | Other expense (income), net [Member]
AOCI Reclassification [Line Items]
Amount of gain (loss) reclassified from AOCI into income/(expense) (effective portion)	1		(1)
Cash flow hedges [Member] | Currency exchange contracts [Member] | Cost of goods sold [Member]
AOCI Reclassification [Line Items]
Amount of gain (loss) reclassified from AOCI into income/(expense) (effective portion)	1	[2]	1	[2]
Cash flow hedges [Member] | Currency exchange contracts [Member] | Net sales [Member]
AOCI Reclassification [Line Items]
Amount of gain (loss) reclassified from AOCI into income/(expense) (effective portion)	$ 4		$ 0

[1] Includes amounts related to de-designated electricity swap. AOCI related to this swap is amortized to income over the remaining term of the hedged item.

[2] "Cost of goods sold" is exclusive of depreciation and amortization.

[3] Includes amounts related to natural gas swaps.