Financial Instruments and Commodity Contracts (Details 4) (Cash flow hedges [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in OCI (Effective Portion)	$ 11	$ (24)
Amount of Gain (Loss) Recognized in “Other (Income) Expense, net” (Ineffective and Excluded Portion)	2	11
Aluminium contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in OCI (Effective Portion)	(21)	29
Amount of Gain (Loss) Recognized in “Other (Income) Expense, net” (Ineffective and Excluded Portion)	3	11
Currency exchange contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in OCI (Effective Portion)	32	(51)
Amount of Gain (Loss) Recognized in “Other (Income) Expense, net” (Ineffective and Excluded Portion)	(1)	0
Energy contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in OCI (Effective Portion)	0	(2)
Amount of Gain (Loss) Recognized in “Other (Income) Expense, net” (Ineffective and Excluded Portion)	$ 0	$ 0