Financial Instruments and Commodity Contracts (Details 4) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in OCI (Effective Portion)	$ (45)	$ 14	$ (34)	$ (10)
Amount of Gain (Loss) Recognized in “Other Expense (Income), net” (Ineffective and Excluded Portion)	7	8	9	19
Cash flow hedges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in OCI (Effective Portion)	(49)	16	(38)	(8)
Amount of Gain (Loss) Recognized in “Other Expense (Income), net” (Ineffective and Excluded Portion)	7	8	9	19
Cash flow hedges [Member] | Aluminum Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in OCI (Effective Portion)	(27)	(10)	(48)	19
Amount of Gain (Loss) Recognized in “Other Expense (Income), net” (Ineffective and Excluded Portion)	7	7	10	18
Cash flow hedges [Member] | Currency Exchange Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in OCI (Effective Portion)	(19)	26	13	(25)
Amount of Gain (Loss) Recognized in “Other Expense (Income), net” (Ineffective and Excluded Portion)	0	1	(1)	1
Cash flow hedges [Member] | Energy Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in OCI (Effective Portion)	(3)	0	(3)	(2)
Amount of Gain (Loss) Recognized in “Other Expense (Income), net” (Ineffective and Excluded Portion)	0	0	0	0
Net Investment Hedging [Member] | Currency Exchange Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in OCI (Effective Portion)	4	(2)	4	(2)
Amount of Gain (Loss) Recognized in “Other Expense (Income), net” (Ineffective and Excluded Portion)	$ 0	$ 0	$ 0	$ 0