Postretirement Benefit Plans (Postretirement Changes Recognized in AOCI) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Beginning balance in Accumulated other comprehensive (loss) income	$ (268)	$ (301)
Curtailments and settlements	0	1
Plan amendment	3	5
Net actuarial (loss) gain	(249)	8
Amortization of prior service credits	(2)	(2)
Amortization of actuarial loss	24	31
Effect of currency exchange	53	(10)
Total postretirement amounts recognized in Accumulated other comprehensive (loss) income	(439)	(268)
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Beginning balance in Accumulated other comprehensive (loss) income	56	(31)
Curtailments and settlements	0	0
Plan amendment	(11)	89
Net actuarial (loss) gain	5	15
Amortization of prior service credits	(37)	(24)
Amortization of actuarial loss	5	7
Effect of currency exchange	0	0
Total postretirement amounts recognized in Accumulated other comprehensive (loss) income	$ 18	$ 56