Debt And Financing Activities (Long-Term Debt) (Narrative) (Details) (USD $)	1 Months Ended	12 Months Ended			1 Months Ended	12 Months Ended					12 Months Ended				12 Months Ended			1 Months Ended
	Feb. 28, 2011	Mar. 31, 2012 D	Mar. 31, 2011	Mar. 31, 2010	Feb. 29, 2012 7.75% Notes due February, 2012 [Member]	Mar. 31, 2012 7.75% Notes due February, 2012 [Member]	Mar. 31, 2012 5.25% Notes due March, 2013 [Member]	Mar. 31, 2012 6.50% Notes due February, 2014 [Member]	Mar. 31, 2012 3.25% Notes due March, 2016 [Member]	Feb. 28, 2011 3.25% Notes due March, 2016 [Member]	Mar. 31, 2012 5.70% Notes due March, 2017 [Member]	Mar. 31, 2012 7.50% Notes due February, 2019 [Member]	Mar. 31, 2012 4.75% Notes dues March, 2021 [Member]	Feb. 28, 2011 4.75% Notes dues March, 2021 [Member]	Mar. 31, 2012 7.65% Debentures due March, 2027 [Member]	Mar. 31, 2012 6.00% Notes due March, 2041 [Member]	Feb. 28, 2011 6.00% Notes due March, 2041 [Member]	Mar. 31, 2010 9.13% Series C Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate on debt					7.75%	7.75%	5.25%	6.50%	3.25%		5.70%	7.50%	4.75%	4.75%	7.65%	6.00%		9.13%
Aggregate principal amount of debt										$ 600,000,000				$ 600,000,000			$ 500,000,000
Maturity date						Feb. 01, 2012	Mar. 01, 2013	Feb. 15, 2014	Mar. 01, 2016		Mar. 01, 2017	Feb. 15, 2019	Mar. 01, 2021		Mar. 01, 2027	Mar. 01, 2041
Net proceeds from issuance of long-term debt	1,673,000,000	0	1,689,000,000	0
Number of days notice before notes can be redeemed		30
Amount repaid					400,000,000													215,000,000
Future principal payments of long-term debt in 2013		508,000,000
Future principal payments of long-term debt in 2014		351,000,000
Future principal payments of long-term debt in 2015		2,000,000
Future principal payments of long-term debt in 2016		600,000,000
Future principal payments of long-term debt in 2017		500,000,000
Future principal payments of long-term debt, thereafter		$ 1,619,000,000
Contingent purchase offer, Series		101.00%