Debt and Financing Activities - Schedule Of Long-Term Debt (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 05, 2014
Debt Instrument [Line Items]
Total debt	$ 8,147	$ 9,709
Less current portion	(1,612)	(1,529)
Total long-term debt	6,535	8,180
Floating Rate Notes due September 10, 2015
Debt Instrument [Line Items]
Total debt	$ 0	400
Debt maturity date	Sep. 10, 2015
0.95% Notes due December 4, 2015
Debt Instrument [Line Items]
Total debt	$ 0	500
Debt interest rate	0.95%
Debt maturity date	Dec. 04, 2015
3.25% Notes due March 1, 2016
Debt Instrument [Line Items]
Total debt	$ 0	600
Debt interest rate	3.25%
Debt maturity date	Mar. 01, 2016
5.70% Notes due March 1, 2017
Debt Instrument [Line Items]
Total debt	$ 500	500
Debt interest rate	5.70%
Debt maturity date	Mar. 01, 2017
1.29% Notes due March 10, 2017
Debt Instrument [Line Items]
Total debt	$ 700	700
Debt interest rate	1.29%		1.29%
Debt maturity date	Mar. 10, 2017
1.40% Notes due March 15, 2018
Debt Instrument [Line Items]
Total debt	$ 500	499
Debt interest rate	1.40%
Debt maturity date	Mar. 15, 2018
7.50% Notes due February 15, 2019
Debt Instrument [Line Items]
Total debt	$ 350	349
Debt interest rate	7.50%
Debt maturity date	Feb. 15, 2019
2.28% Notes due March 15, 2019
Debt Instrument [Line Items]
Total debt	$ 1,100	1,100
Debt interest rate	2.28%		2.28%
Debt maturity date	Mar. 15, 2019
4.75% Notes due March 1, 2021
Debt Instrument [Line Items]
Total debt	$ 599	599
Debt interest rate	4.75%
Debt maturity date	Mar. 01, 2021
2.70% Notes due December 15, 2022
Debt Instrument [Line Items]
Total debt	$ 400	400
Debt interest rate	2.70%
Debt maturity date	Dec. 15, 2022
2.85% Notes due March 15, 2023
Debt Instrument [Line Items]
Total debt	$ 400	400
Debt interest rate	2.85%
Debt maturity date	Mar. 15, 2023
3.80% Notes due March 15, 2024
Debt Instrument [Line Items]
Total debt	$ 1,100	1,100
Debt interest rate	3.80%		3.80%
Debt maturity date	Mar. 15, 2024
7.65% Debentures due March 1, 2027
Debt Instrument [Line Items]
Total debt	$ 175	175
Debt interest rate	7.65%
Debt maturity date	Mar. 01, 2027
6.00% Notes due March 1, 2041
Debt Instrument [Line Items]
Total debt	$ 493	493
Debt interest rate	6.00%
Debt maturity date	Mar. 01, 2041
4.88% Notes due March 15, 2044
Debt Instrument [Line Items]
Total debt	$ 800	800
Debt interest rate	4.88%		4.88%
Debt maturity date	Mar. 15, 2044
4.00% Bonds due October 18, 2016
Debt Instrument [Line Items]
Total debt	$ 403	388
Debt interest rate	4.00%
Debt maturity date	Oct. 18, 2016
4.50% Bonds due April 26, 2017
Debt Instrument [Line Items]
Total debt	$ 583	563
Debt interest rate	4.50%
Debt maturity date	Apr. 26, 2017
Lease and other obligations
Debt Instrument [Line Items]
Total debt	$ 44	$ 143