Debt (Details) (USD $)	3 Months Ended	12 Months Ended
	Sep. 30, 2014	Mar. 31, 2014
Debt Instrument [Line Items]
Debt	$ 87,769,000,000	$ 85,367,000,000
Weighted average contractual interest rate	1.27%	1.26%
Commercial paper [Member]
Debt Instrument [Line Items]
Debt	27,138,000,000	27,709,000,000
Weighted average contractual interest rate	0.18%	0.18%
Commercial paper average remaining maturity	As of September 30, 2014, our commercial paper had a weighted average remaining maturity of 79 days.
Unsecured notes and loans payable [Member]
Debt Instrument [Line Items]
Debt	52,576,000,000	49,075,000,000
Weighted average contractual interest rate	1.94%	1.99%
Debt denominated in foreign currency	12,200,000,000	12,600,000,000
Unsecured notes and loans payable [Member] | Floating rate [Member]
Debt Instrument [Line Items]
Debt	17,600,000,000	17,600,000,000
Contractual interest rate, minimum	0.00%	0.00%
Contractual interest rate, maximum	3.50%	3.30%
Unsecured notes and loans payable [Member] | Fixed rate [Member]
Debt Instrument [Line Items]
Debt	35,100,000,000	31,900,000,000
Contractual interest rate, minimum	0.50%	0.50%
Contractual interest rate, maximum	9.40%	9.40%
Secured notes and loans payable [Member]
Debt Instrument [Line Items]
Debt	7,887,000,000	8,158,000,000
Weighted average contractual interest rate	0.55%	0.54%
Debt maturity dates	As of September 30, 2014, our notes and loans payable mature on various dates through fiscal 2047.
Secured notes and loans payable [Member] | Floating rate [Member]
Debt Instrument [Line Items]
Contractual interest rate, minimum	0.40%	0.40%
Contractual interest rate, maximum	1.50%	1.60%
Secured notes and loans payable [Member] | Fixed rate [Member]
Debt Instrument [Line Items]
Contractual interest rate, minimum	0.40%	0.40%
Contractual interest rate, maximum	1.50%	1.60%
Carrying value adjustment [Member]
Debt Instrument [Line Items]
Debt	$ 168,000,000	$ 425,000,000