Debt and Credit Facilities - Additional Information (Details) - USD ($)	1 Months Ended		12 Months Ended
	Nov. 30, 2019	Jun. 30, 2019	Mar. 31, 2020	Mar. 31, 2019
364 Day Credit Agreement Expiring 2021 [Member]
Line Of Credit Facility [Line Items]
Initiation date	Nov. 30, 2019
Maximum borrowing capacity	$ 5,000,000,000
Credit facilities amount outstanding			$ 0	$ 0
Three Year Agreement Expiring 2023 [Member]
Line Of Credit Facility [Line Items]
Initiation date	Nov. 30, 2019
Maximum borrowing capacity	$ 5,000,000,000
Credit facilities amount outstanding			0	0
Five Year Agreement Expiring 2025 [Member]
Line Of Credit Facility [Line Items]
Initiation date	Nov. 30, 2019
Maximum borrowing capacity	$ 5,000,000,000
Credit facilities amount outstanding			0	0
Total Committed Bank Credit Facilities [Member]
Line Of Credit Facility [Line Items]
Maximum borrowing capacity			4,600,000,000
Credit facilities amount outstanding			0	$ 0
Committed Bank Credit Facility Expiring 2021 [Member]
Line Of Credit Facility [Line Items]
Maximum borrowing capacity			2,500,000,000
Committed Bank Credit Facility Expiring 2023 [Member]
Line Of Credit Facility [Line Items]
Maximum borrowing capacity			2,100,000,000
Three Year Revolving Credit Facility Expiring 2022 [Member]
Line Of Credit Facility [Line Items]
Maximum borrowing capacity			5,000,000,000
Credit facilities amount outstanding			$ 3,000,000,000
Credit facilities interest rate			1.86%
Credit facility, maturity date			Sep. 30, 2020
Secured notes and loans payable [Member]
Line Of Credit Facility [Line Items]
New revolving asset backed securities period		5 years
Secured notes and loans payable [Member] | Maximum [Member]
Line Of Credit Facility [Line Items]
Percentage of initial principal amount		50.00%