Debt and Credit Facilities - Debt and Related Weighted Average Contractual Interest Rates (Details) - USD ($) $ in Millions	Dec. 31, 2021	Mar. 31, 2021
Debt Instrument [Line Items]
Debt, Face value	$ 110,407	$ 110,015
Debt, Carrying value	$ 110,122	$ 109,725
Weighted average contractual interest rates	1.10%	1.31%
Unsecured notes and loans payable [Member]
Debt Instrument [Line Items]
Debt, Face value	$ 82,293	$ 85,759
Debt, Carrying value	$ 82,054	$ 85,513
Weighted average contractual interest rates	1.17%	1.31%
Secured notes and loans payable [Member]
Debt Instrument [Line Items]
Debt, Face value	$ 28,114	$ 24,256
Debt, Carrying value	$ 28,068	$ 24,212
Weighted average contractual interest rates	0.91%	1.29%