Debt and Financing Activities (Long-Term Debt) (Narrative) (Details) (USD $) In Millions, unless otherwise specified	0 Months Ended		1 Months Ended	12 Months Ended
	Mar. 05, 2014	Dec. 04, 2012	Mar. 31, 2013	Mar. 31, 2015 D	Mar. 31, 2014	Mar. 31, 2013
Debt Instrument [Line Items]
Proceeds from issuances of long-term debt	$ 4,068	$ 892	$ 891	$ 3	$ 4,124	$ 1,798
Days notice for redemption prior to maturity				30
Redemption purchase offer				101.00%
Long-term debt				9,709	10,346
Future principal payments of long-term debt in 2016					1,529
Future principal payments of long-term debt in 2017					1,619
Future principal payments of long-term debt in 2018					1,086
Future principal payments of long-term debt in 2019					1,474
Future principal payments of long-term debt in 2020					19
Future principal payments of long-term debt, thereafter					3,982
Floating Rate Notes Due September 10, 2015 [Member]
Debt Instrument [Line Items]
Debt face value					400
Debt variable interest rate				0.66%
Debt maturity date				Sep. 10, 2015	Sep. 10, 2015
Long-term debt				400	400
1.29% Notes Due March 10, 2017 [Member]
Debt Instrument [Line Items]
Debt face value					700
Debt interest rate				1.29%	1.29%
Debt maturity date				Mar. 10, 2017	Mar. 10, 2017
Long-term debt				700	700
2.28% Notes Due March 15, 2019 [Member]
Debt Instrument [Line Items]
Debt face value					1,100
Debt interest rate				2.28%	2.28%
Debt maturity date				Mar. 15, 2019	Mar. 15, 2019
Long-term debt				1,100	1,100
3.80% Notes Due March 15, 2024 [Member]
Debt Instrument [Line Items]
Debt face value					1,100
Debt interest rate				3.80%	3.80%
Debt maturity date				Mar. 15, 2024	Mar. 15, 2024
Long-term debt				1,100	1,100
4.88% Notes Due March 15, 2044 [Member]
Debt Instrument [Line Items]
Debt face value					800
Debt interest rate				4.88%	4.88%
Debt maturity date				Mar. 15, 2044	Mar. 15, 2044
Long-term debt				800	800
1.40% Notes Due March 15, 2018 [Member]
Debt Instrument [Line Items]
Debt face value			500			500
Debt interest rate			1.40%	1.40%	1.40%	1.40%
Debt maturity date				Mar. 15, 2018	Mar. 15, 2018	Mar. 15, 2018
Long-term debt				499	499
2.85% Notes Due March 15, 2023 [Member]
Debt Instrument [Line Items]
Debt face value			400			400
Debt interest rate			2.85%	2.85%	2.85%	2.85%
Debt maturity date				Mar. 15, 2023	Mar. 15, 2023	Mar. 15, 2023
Long-term debt				400	400
0.95% Notes Due December 4, 2015 [Member]
Debt Instrument [Line Items]
Debt face value			500			500
Debt interest rate			0.95%	0.95%	0.95%	0.95%
Debt maturity date				Dec. 04, 2015	Dec. 04, 2015	Dec. 04, 2015
Long-term debt				500	499
2.70% Notes Due December 15, 2022 [Member]
Debt Instrument [Line Items]
Debt face value			400			400
Debt interest rate			2.70%	2.70%	2.70%	2.70%
Debt maturity date				Dec. 15, 2022	Dec. 15, 2022	Dec. 15, 2022
Long-term debt				400	400
6.50% Notes Due February 15, 2014 [Member]
Debt Instrument [Line Items]
Debt interest rate					6.50%
Debt repayment amount					350
5.25% Notes Due March 1, 2013 [Member]
Debt Instrument [Line Items]
Debt interest rate					5.25%
Debt repayment amount					500
4.00% Bonds Due October 18, 2016 [Member]
Debt Instrument [Line Items]
Debt interest rate				4.00%	4.00%
Debt maturity date				Oct. 18, 2016	Oct. 18, 2016
Long-term debt				388	507
4.50% Bonds Due April 26, 2017 [Member]
Debt Instrument [Line Items]
Debt interest rate				4.50%	4.50%
Debt maturity date				Apr. 26, 2017	Apr. 26, 2017
Long-term debt				563	737
4.00% Bonds Due October 18, 2016 and 4.50% Bonds Due April 26, 2017 [Member]
Debt Instrument [Line Items]
Long-term debt				951	1,244
Promissory Notes [Member]
Debt Instrument [Line Items]
Long-term debt				0	297
Term Loan [Member]
Debt Instrument [Line Items]
Debt variable interest rate				1.93%
Debt maturity date				Dec. 15, 2019
Long-term debt				89	100
Senior Notes Due 2022 [Member]
Debt Instrument [Line Items]
Debt interest rate			6.375%			6.375%
Debt maturity date						Jan. 31, 2022
Senior Convertible Notes Due 2014 [Member]
Debt Instrument [Line Items]
Debt interest rate				3.125%
Debt maturity date						Nov. 30, 2014
Senior Notes Due 2022 And Senior Convertible Notes Due 2014 [Member]
Debt Instrument [Line Items]
Debt repayment amount						$ 643
London Interbank Offered Rate (LIBOR) [Member] | Floating Rate Notes Due September 10, 2015 [Member]
Debt Instrument [Line Items]
Debt variable interest rate					0.40%