Debt And Financing Activities (Schedule Of Long-Term Debt) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013
Debt Instrument [Line Items]
Long-term debt	$ 9,709	$ 10,346
Less current portion	(1,529)	(1,417)
Total long-term debt	8,180	8,929
Floating Rate Notes Due September 10, 2015 [Member]
Debt Instrument [Line Items]
Long-term debt	400	400
Debt variable interest rate	0.66%
Debt maturity date	Sep. 10, 2015	Sep. 10, 2015
0.95% Notes Due December 4, 2015 [Member]
Debt Instrument [Line Items]
Long-term debt	500	499
Debt interest rate	0.95%	0.95%	0.95%
Debt maturity date	Dec. 04, 2015	Dec. 04, 2015	Dec. 04, 2015
3.25% Notes Due March 1, 2016 [Member]
Debt Instrument [Line Items]
Long-term debt	600	599
Debt interest rate	3.25%	3.25%
Debt maturity date	Mar. 01, 2016	Mar. 01, 2016
5.70% Notes Due March 1, 2017 [Member]
Debt Instrument [Line Items]
Long-term debt	500	500
Debt interest rate	5.70%	5.70%
Debt maturity date	Mar. 01, 2017	Mar. 01, 2017
1.29% Notes Due March 10, 2017 [Member]
Debt Instrument [Line Items]
Long-term debt	700	700
Debt interest rate	1.29%	1.29%
Debt maturity date	Mar. 10, 2017	Mar. 10, 2017
1.40% Notes Due March 15, 2018 [Member]
Debt Instrument [Line Items]
Long-term debt	499	499
Debt interest rate	1.40%	1.40%	1.40%
Debt maturity date	Mar. 15, 2018	Mar. 15, 2018	Mar. 15, 2018
7.50% Notes Due February 15, 2019 [Member]
Debt Instrument [Line Items]
Long-term debt	349	349
Debt interest rate	7.50%	7.50%
Debt maturity date	Feb. 15, 2019	Feb. 15, 2019
2.28% Notes Due March 15, 2019 [Member]
Debt Instrument [Line Items]
Long-term debt	1,100	1,100
Debt interest rate	2.28%	2.28%
Debt maturity date	Mar. 15, 2019	Mar. 15, 2019
4.75% Notes Due March 1, 2021 [Member]
Debt Instrument [Line Items]
Long-term debt	599	598
Debt interest rate	4.75%	4.75%
Debt maturity date	Mar. 01, 2021	Mar. 01, 2021
2.70% Notes Due December 15, 2022 [Member]
Debt Instrument [Line Items]
Long-term debt	400	400
Debt interest rate	2.70%	2.70%	2.70%
Debt maturity date	Dec. 15, 2022	Dec. 15, 2022	Dec. 15, 2022
2.85% Notes Due March 15, 2023 [Member]
Debt Instrument [Line Items]
Long-term debt	400	400
Debt interest rate	2.85%	2.85%	2.85%
Debt maturity date	Mar. 15, 2023	Mar. 15, 2023	Mar. 15, 2023
3.80% Notes Due March 15, 2024 [Member]
Debt Instrument [Line Items]
Long-term debt	1,100	1,100
Debt interest rate	3.80%	3.80%
Debt maturity date	Mar. 15, 2024	Mar. 15, 2024
7.65% Debentures Due March 1, 2027 [Member]
Debt Instrument [Line Items]
Long-term debt	175	175
Debt interest rate	7.65%	7.65%
Debt maturity date	Mar. 01, 2027	Mar. 01, 2027
6.00% Notes Due March 1, 2041 [Member]
Debt Instrument [Line Items]
Long-term debt	493	493
Debt interest rate	6.00%	6.00%
Debt maturity date	Mar. 01, 2041	Mar. 01, 2041
4.88% Notes Due March 15, 2044 [Member]
Debt Instrument [Line Items]
Long-term debt	800	800
Debt interest rate	4.88%	4.88%
Debt maturity date	Mar. 15, 2044	Mar. 15, 2044
Other Long Term Debt [Member]
Debt Instrument [Line Items]
Long-term debt	26	27
4.00% Bonds Due October 18, 2016 [Member]
Debt Instrument [Line Items]
Long-term debt	388	507
Debt interest rate	4.00%	4.00%
Debt maturity date	Oct. 18, 2016	Oct. 18, 2016
4.50% Bonds Due April 26, 2017 [Member]
Debt Instrument [Line Items]
Long-term debt	563	737
Debt interest rate	4.50%	4.50%
Debt maturity date	Apr. 26, 2017	Apr. 26, 2017
Promissory Notes [Member]
Debt Instrument [Line Items]
Long-term debt	0	297
Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Long-term debt	$ 117	$ 166
London Interbank Offered Rate (LIBOR) [Member] | Floating Rate Notes Due September 10, 2015 [Member]
Debt Instrument [Line Items]
Debt variable interest rate		0.40%