Leases - Components of lease expense (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Lease expense
Operating lease cost	$ 79	$ 151
Amortization of assets	6	10
Interest on lease liabilities	1	1
Variable Lease, Cost	22	42
Total net lease cost	$ 108	$ 204