Leases - Components of balance sheet (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Operating lease right-of-use assets	$ 1,019	$ 0
Current portion of operating lease liabilities	255	0
Operating lease liabilities	758	$ 0
Other Assets [Member]
Finance Lease, Right-of-Use Asset	142
Other Current Liabilities [Member]
Finance Lease, Liability, Current	12
Other Liabilities [Member]
Finance Lease, Liability, Noncurrent	$ 139