Postretirement Benefits (Schedule Of Changes In Benefit Obligations For Postretirement Welfare Plans) (Details) (Other Postretirement Benefit Plan, Defined Benefit [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of period	$ 119	$ 131
Service cost	1	2	2
Interest cost	5	5	6
Actuarial (gain) loss	5	(2)
Benefit payments	(12)	(15)
Defined Benefit Plan, Curtailments	0	(2)
Benefit obligation at end of period (1)	$ 118	$ 119	$ 131