Accumulated Other Comprehensive Income (Loss) (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
Increase (Decrease) in Stockholders' Equity
Balance as of beginning of period	$ (60)		$ (310)		$ (91)		$ (268)
Other comprehensive income before reclassifications	(162)		167		(128)		136
Amounts reclassified from AOCI	28		(5)		25		(16)
Net current-period other comprehensive income (loss)	(134)		162		(103)		120
Balance as of end of period	(194)		(148)		(194)		(148)
Currency Translation [Member]
Increase (Decrease) in Stockholders' Equity
Balance as of beginning of period	115		(35)		89		(33)
Other comprehensive income before reclassifications	(131)		94		(105)		92
Amounts reclassified from AOCI	0		0		0		0
Net current-period other comprehensive income (loss)	(131)		94		(105)		92
Balance as of end of period	(16)		59		(16)		59
Cash Flow Hedges [Member]
Increase (Decrease) in Stockholders' Equity
Balance as of beginning of period	(7)	[1]	(46)	[1]	(20)	[1]	(2)	[1]
Other comprehensive income before reclassifications	(39)	[1]	15	[1]	(26)	[1]	(14)	[1]
Amounts reclassified from AOCI	27	[1]	(8)	[1]	27	[1]	(23)	[1]
Net current-period other comprehensive income (loss)	(12)	[1]	7	[1]	1	[1]	(37)	[1]
Balance as of end of period	(19)	[1]	(39)	[1]	(19)	[1]	(39)	[1]
Postretirement Benefit Plans [Member]
Increase (Decrease) in Stockholders' Equity
Balance as of beginning of period	(168)	[2]	(229)	[2]	(160)	[2]	(233)	[2]
Other comprehensive income before reclassifications	8	[2]	58	[2]	3	[2]	58	[2]
Amounts reclassified from AOCI	1	[2]	3	[2]	(2)	[2]	7	[2]
Net current-period other comprehensive income (loss)	9	[2]	61	[2]	1	[2]	65	[2]
Balance as of end of period	$ (159)	[2]	$ (168)	[2]	$ (159)	[2]	$ (168)	[2]

[1] For additional information on our cash flow hedges see Note 11 - Financial Instruments and Commodity Contracts.

[2] For additional information on our postretirement benefit plans see Note 9 - Postretirement Benefit Plans.