Debt and Credit Facilities - Debt and Related Weighted Average Contractual Interest Rates (Details) - USD ($) $ in Millions	Mar. 31, 2021	Mar. 31, 2020
Debt Instrument [Line Items]
Debt, Face value	$ 110,015	$ 98,074
Debt, Carrying value	$ 109,725	$ 97,740
Weighted average contractual interest rates	1.31%	2.08%
Unsecured notes and loans payable [Member]
Debt Instrument [Line Items]
Debt, Face value	$ 85,759	$ 83,477
Debt, Carrying value	$ 85,513	$ 83,172
Weighted average contractual interest rates	1.31%	2.07%
Secured notes and loans payable [Member]
Debt Instrument [Line Items]
Debt, Face value	$ 24,256	$ 14,597
Debt, Carrying value	$ 24,212	$ 14,568
Weighted average contractual interest rates	1.29%	2.13%