Leases - Components of Lease Expense (Details) $ in Millions	3 Months Ended
	Jun. 30, 2019 USD ($)
Leases [Abstract]
Operating lease cost	$ 176
Short-term lease cost	10
Variable lease cost	15
Sublease income	(9)
Total operating costs	192
Finance lease cost:
Amortization of right-of-use assets	109
Interest on lease liabilities	17
Total finance lease cost	$ 126