Accumulated Other Comprehensive Income (Loss) AOCI Reclassifications Impact (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other expense (income), net	$ (18)		$ 5		$ (23)		$ 15
Cost of goods sold	2,483		2,074		4,812		4,172
Net sales	2,831		2,414		5,511		4,815
Income before taxes	36		49		95		66
Income tax provision	2		(26)		(22)		(29)
Net income	38		23		73		37
Cash flow hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before taxes	(43)		13		(43)		35
Income tax provision	16		(5)		16		(12)
Net income	(27)		8		(27)		23
Cash flow hedges [Member] | Other expense (income), net [Member] | Energy Contracts [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other expense (income), net	2	[1]	2	[1]	3	[1]	3	[1]
Cash flow hedges [Member] | Other expense (income), net [Member] | Currency Exchange Contract [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other expense (income), net	2		0		1		1
Cash flow hedges [Member] | Cost of goods sold [Member] | Energy Contracts [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Cost of goods sold	0	[2],[3]	0	[2],[3]	1	[2],[3]	0	[2],[3]
Cash flow hedges [Member] | Cost of goods sold [Member] | Aluminum Contracts [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Cost of goods sold	(45)	[2]	18	[2]	(51)	[2]	39	[2]
Cash flow hedges [Member] | Cost of goods sold [Member] | Currency Exchange Contract [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Cost of goods sold	1	[2]	(5)	[2]	2	[2]	(4)	[2]
Cash flow hedges [Member] | Net sales [Member] | Aluminum Contracts [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net sales	0		2		0		4
Cash flow hedges [Member] | Net sales [Member] | Currency Exchange Contract [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net sales	$ 5		$ 0		$ 9		$ 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.