Leases - Components of Lease Expense (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Dec. 31, 2019	Dec. 31, 2019
Leases [Abstract]
Operating lease expense	$ 545	$ 1,622
Amortization of right-to-use assets	18	55
Interest on lease liabilities	1	2
Total finance lease expense	19	57
Variable lease expense	23	65
Total lease expense	$ 587	$ 1,744