Debt - Additional Information (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Dec. 31, 2015	Mar. 31, 2015
Debt Instrument [Line Items]
Debt	$ 94,708	$ 90,231
Increase (decrease) in carrying value adjustment on debt	$ (34)
Commercial paper [Member]
Debt Instrument [Line Items]
Commercial paper weighted average remaining maturity	As of December 31, 2015, our commercial paper had a weighted average remaining maturity of 80 days
Commercial paper average remaining maturity period	80 days
Debt	$ 26,847	27,006
Secured notes and loans payable [Member]
Debt Instrument [Line Items]
Debt maturity dates	As of December 31, 2015,our notes and loans payable mature on various dates through fiscal 2047.
Debt maturity year	2047
Debt	$ 14,030	$ 10,837
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	1.70%	1.50%
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	1.70%	1.50%
Unsecured notes and loans payable [Member]
Debt Instrument [Line Items]
Debt	$ 53,784	$ 52,307
Debt denominated in foreign currency	13,800	12,400
Unsecured notes and loans payable [Member] | Floating rate [Member]
Debt Instrument [Line Items]
Debt	$ 18,400	$ 17,400
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	$ 35,400	$ 35,000
Contractual interest rate, minimum	0.80%	0.80%
Contractual interest rate, maximum	9.40%	9.40%