(Change in Benefit Obligation) (Details) - USD ($) $ in Millions	5 Months Ended	12 Months Ended
	Aug. 31, 2013	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Amendments	$ 97	$ 11
Pension Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period		1,868	$ 1,863
Service cost		45	47	$ 43
Interest cost		59	59	66
Members’ contributions		4	5
Benefits paid		(74)	(65)
Amendments		2	0
Curtailments, settlements and special termination benefits		(4)	(1)
Actuarial losses (gains)		35	(43)
Other		(4)	(1)
Currency (gains) losses		(66)	4
Benefit obligation at end of period		1,865	1,868	1,863
Pension Benefits [Member] | Funded Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period		1,578
Benefit obligation at end of period		1,594	1,578
Pension Benefits [Member] | Unfunded Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period		290
Benefit obligation at end of period		271	290
Other Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period		151	139
Service cost		6	5	5
Interest cost		6	5	5
Members’ contributions		0	0
Benefits paid		(8)	(10)	(10)
Amendments		0	0
Curtailments, settlements and special termination benefits		0	0
Actuarial losses (gains)		(3)	11
Other		0	0
Currency (gains) losses		1	1
Benefit obligation at end of period		153	151	$ 139
Other Benefits [Member] | Funded Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period		0
Benefit obligation at end of period		0	0
Other Benefits [Member] | Unfunded Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period		151
Benefit obligation at end of period		$ 153	$ 151