Leases - Components of balance sheet (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Operating lease right-of-use assets	$ 978	$ 0
Current portion of operating lease liabilities	215	0
Operating lease liabilities	761	$ 0
Other Assets [Member]
Finance Lease, Right-of-Use Asset	141
Other Current Liabilities [Member]
Finance Lease, Liability, Current	17
Other Liabilities [Member]
Finance Lease, Liability, Noncurrent	$ 136