Postretirement Benefit Plans (Postretirement Changes Recognized in AOCI) (Details) - USD ($)	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Beginning balance in Accumulated other comprehensive (loss) income	$ (435,000,000)	$ (439,000,000)
Curtailments, settlements, and special termination benefits	1,000,000	0
Net actuarial gain (loss)	11,000,000	(25,000,000)
Prior service cost	(2,000,000)	0
Amortization of prior service credits	(2,000,000)	(2,000,000)
Amortization of actuarial loss	43,000,000	41,000,000
Effect of currency exchange	13,000,000	(10,000,000)
Total postretirement amounts recognized in Accumulated other comprehensive (loss) income	(371,000,000)	(435,000,000)
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Beginning balance in Accumulated other comprehensive (loss) income	(16,000,000)	18,000,000
Curtailments, settlements, and special termination benefits	0	0
Net actuarial gain (loss)	2,000,000	(11,000,000)
Prior service cost	0	0
Amortization of prior service credits	1,000,000	(27,000,000)
Amortization of actuarial loss	4,000,000	4,000,000
Effect of currency exchange	0	0
Total postretirement amounts recognized in Accumulated other comprehensive (loss) income	$ (9,000,000)	$ (16,000,000)