SUMMARY OF ACCOUNTING POLICIES - Recently Adopted Accounting Pronouncements (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other investing activities, net	$ 3,585,901	$ 4,619,933	$ 4,972,017
Asset-backed Securities
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other investing activities, net	3,600,000	$ 4,600,000	$ 5,000,000
Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease liability	550,000
Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease liability	$ 750,000