Leases - Supplemental Cash Flows (Details) $ in Millions	3 Months Ended
	Jun. 30, 2019 USD ($)
Leases [Abstract]
Operating cash flows from finance leases	$ 2
Operating cash flows from operating leases	576
Financing cash flows from finance leases	1
Total cash paid for amounts included in the measurement of lease liabilities	579
Operating lease right-of-use assets obtained in exchange for lease obligations:	$ 113