Debt and Credit Facilities - Debt and Related Weighted Average Contractual Interest Rates (Details) - USD ($) $ in Millions	Jun. 30, 2021	Mar. 31, 2021
Debt Instrument [Line Items]
Debt, Face value	$ 109,434	$ 110,015
Debt, Carrying value	$ 109,133	$ 109,725
Weighted average contractual interest rates	1.20%	1.31%
Unsecured notes and loans payable [Member]
Debt Instrument [Line Items]
Debt, Face value	$ 84,483	$ 85,759
Debt, Carrying value	$ 84,233	$ 85,513
Weighted average contractual interest rates	1.21%	1.31%
Secured notes and loans payable [Member]
Debt Instrument [Line Items]
Debt, Face value	$ 24,951	$ 24,256
Debt, Carrying value	$ 24,900	$ 24,212
Weighted average contractual interest rates	1.15%	1.29%