Accumulated Other Comprehensive Loss (Components of AOCI) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Increase (Decrease) in AOCI [Roll Forward]
Accumulated other comprehensive income (loss), beginning of period	$ (91)	$ (268)	$ (191)
Other comprehensive income before reclassifications	(494)	193	(80)
Amounts reclassified from AOCI, net	24	(16)	3
Net current-period other comprehensive (loss) income	(470)	177	(77)
Accumulated other comprehensive income (loss), end of period	(561)	(91)	(268)
Currency Translation [Member]
Increase (Decrease) in AOCI [Roll Forward]
Accumulated other comprehensive income (loss), beginning of period	89	(33)	20
Other comprehensive income before reclassifications	(302)	122	(42)
Amounts reclassified from AOCI, net	0	0	(11)	(11)
Net current-period other comprehensive (loss) income	(302)	122	(53)
Accumulated other comprehensive income (loss), end of period	(213)	89	(33)	20
Cash Flow Hedges [Member]
Increase (Decrease) in AOCI [Roll Forward]
Accumulated other comprehensive income (loss), beginning of period	(20)	(2)	(7)
Other comprehensive income before reclassifications	(74)	7	11
Amounts reclassified from AOCI, net	31	(25)	(6)
Net current-period other comprehensive (loss) income	(43)	(18)	5
Accumulated other comprehensive income (loss), end of period	(63)	(20)	(2)
Postretirement Benefit Plans [Member]
Increase (Decrease) in AOCI [Roll Forward]
Accumulated other comprehensive income (loss), beginning of period	(160)	(233)	(204)
Other comprehensive income before reclassifications	(118)	64	(49)
Amounts reclassified from AOCI, net	(7)	9	20
Net current-period other comprehensive (loss) income	(125)	73	(29)
Accumulated other comprehensive income (loss), end of period	(285)	(160)	(233)
Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) [Member] \| Noncontrolling Interest [Member]
Increase (Decrease) in AOCI [Roll Forward]
Accumulated other comprehensive income (loss), end of period	$ 9

- Definition

Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

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