Leases - Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Leases [Abstract]
Operating lease right-of-use assets	$ 2,423	$ 0
Accounts payable and other current liabilities	460
Operating lease liabilities	1,678	$ 0
Total operating lease liabilities	2,138
Property and equipment	794
Accumulated depreciation	(340)
Property and equipment, net	454
Long-term debt due within one year	48
Long-term debt	337
Total finance lease liabilities	$ 385