Leases - Supplemental Balance Sheet Information - Operating Leases (Details) $ in Millions	Mar. 31, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets	$ 1,323
Operating lease liability, current	178
Operating lease liabilities, non-current	1,225
Total operating lease liabilities	1,403
Operating Lease Excluding Finance Obligation
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets	1,323
Operating lease liability, current	178
Operating lease liabilities, non-current	1,225
Total operating lease liabilities	$ 1,403