Pension Benefits (Schedule Of Reconciliation Of Level 3 Plan Assets Held) (Details) (Pension Plans, Defined Benefit [Member], USD $) In Millions, unless otherwise specified				12 Months Ended				12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2013 Fair Value, Inputs, Level 3 [Member]	Mar. 31, 2012 Fair Value, Inputs, Level 3 [Member]	Mar. 31, 2013 Real Estate Funds [Member]	Mar. 31, 2012 Real Estate Funds [Member]	Mar. 31, 2013 Real Estate Funds [Member] Fair Value, Inputs, Level 3 [Member]	Mar. 31, 2012 Real Estate Funds [Member] Fair Value, Inputs, Level 3 [Member]	Mar. 31, 2013 Hedge Funds [Member] Fair Value, Inputs, Level 3 [Member]	Mar. 31, 2012 Hedge Funds [Member] Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of period	$ 425	$ 410	$ 416	$ 17	$ 10	$ 19	$ 17	$ 17	$ 5	$ 0	$ 5
Unrealized gain on plan assets still held				1	1			1	1	0	0
Purchases, sales and settlements				1	6			1	11	0	(5)
Fair value of plan assets at end of period	$ 425	$ 410	$ 416	$ 19	$ 17	$ 19	$ 17	$ 19	$ 17	$ 0	$ 0