Income Taxes (Reconciliation Between Effective Tax Rate On Income From Continuing Operations And Statutory Tax Rate) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013
Income Tax Disclosure [Abstract]
Income tax expense at federal statutory rate	$ 930	$ 760	$ 683
State income taxes net of federal tax benefit	81	57	58
Foreign income taxed at various rates	(247)	(177)	(143)
Canadian litigation	0	122	0
Effective Income Tax Rate Reconciliation, Tax Contingency, Other, Amount	58	0	0
Unrecognized tax benefits and settlements	10	(6)	1
Tax credits	(10)	(6)	(13)
Other, net	(7)	7	1
Income tax expense	$ 815	$ 757	$ 587