Debt and Financing Activities - Schedule Of Long-Term Debt (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 26, 2018	Feb. 16, 2018	Feb. 12, 2018	Feb. 07, 2018	Mar. 31, 2017	Feb. 17, 2017
Debt Instrument [Line Items]
Total debt	$ 7,880					$ 8,362
Less: Current portion	(1,129)					(1,057)
Total long-term debt	6,751					7,305
Notes | 1.40% Notes due March 15, 2018
Debt Instrument [Line Items]
Total debt	$ 0					500
Debt interest rate (percent)	1.40%
Debt maturity date	Mar. 15, 2018
Notes | 7.50% Notes due February 15, 2019
Debt Instrument [Line Items]
Total debt	$ 0					350
Debt interest rate (percent)	7.50%	7.50%			7.50%
Debt maturity date	Feb. 15, 2019
Notes | 2.28% Notes due March 15, 2019
Debt Instrument [Line Items]
Total debt	$ 1,100					1,100
Debt interest rate (percent)	2.28%
Debt maturity date	Mar. 15, 2019
Notes | 4.75% Notes due March 1, 2021
Debt Instrument [Line Items]
Total debt	$ 323					599
Debt interest rate (percent)	4.75%				4.75%
Debt maturity date	Mar. 01, 2021
Notes | 2.70% Notes due December 15, 2022
Debt Instrument [Line Items]
Total debt	$ 400					400
Debt interest rate (percent)	2.70%
Debt maturity date	Dec. 15, 2022
Notes | 2.85% Notes due March 15, 2023
Debt Instrument [Line Items]
Total debt	$ 400					400
Debt interest rate (percent)	2.85%
Debt maturity date	Mar. 15, 2023
Notes | 3.80% Notes due March 15, 2024
Debt Instrument [Line Items]
Total debt	$ 1,100					1,100
Debt interest rate (percent)	3.80%
Debt maturity date	Mar. 15, 2024
Notes | 7.65% Debentures due March 1, 2027
Debt Instrument [Line Items]
Total debt	$ 167					175
Debt interest rate (percent)	7.65%				7.65%
Debt maturity date	Mar. 01, 2027
Notes | 3.95% Notes due February 16, 2028
Debt Instrument [Line Items]
Total debt	$ 600					0
Debt interest rate (percent)	3.95%		3.95%
Debt maturity date	Feb. 16, 2028
Notes | 6.00% Notes due March 1, 2041
Debt Instrument [Line Items]
Total debt	$ 282					493
Debt interest rate (percent)	6.00%				6.00%
Debt maturity date	Mar. 01, 2041
Notes | 4.88% Notes due March 15, 2044
Debt Instrument [Line Items]
Total debt	$ 411					800
Debt interest rate (percent)	4.88%				4.88%
Debt maturity date	Mar. 15, 2044
Notes | 4.50% Euro Bonds due April 26, 2017
Debt Instrument [Line Items]
Total debt	$ 0					533
Debt interest rate (percent)	4.50%
Debt maturity date	Apr. 26, 2017
Notes | Floating Rate Euro Notes Due February Twelve Two Thousand and Twenty [Member]
Debt Instrument [Line Items]
Total debt	$ 337					0
Notes | 0.63% Euro Notes due August 17, 2021
Debt Instrument [Line Items]
Total debt	$ 695					638
Debt interest rate (percent)	0.63%						0.63%
Debt maturity date	Aug. 17, 2021
Notes | 1.50% Euro Notes due November 17, 2025
Debt Instrument [Line Items]
Total debt	$ 691					635
Debt interest rate (percent)	1.50%						1.50%
Debt maturity date	Nov. 17, 2025
Notes | 1.63% Euro Notes due October 30, 2026
Debt Instrument [Line Items]
Total debt	$ 669					0
Debt interest rate (percent)	1.63%			1.63%
Debt maturity date	Oct. 30, 2026
Notes | 3.13% Sterling Notes due February 17, 2029
Debt Instrument [Line Items]
Total debt	$ 630					564
Debt interest rate (percent)	3.13%						3.13%
Debt maturity date	Feb. 17, 2029
Lease and other obligations
Debt Instrument [Line Items]
Total debt	$ 75					$ 75