Leases - Supplemental cash flow and other information (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases		$ 231
Operating cash flows from finance leases		1
Financing cash flows from finance leases		12
Right of use assets obtained in exchange for lease liabilities:
Operating leases		288
Finance leases		58
Gain on sale leaseback transactions, net	$ 59	$ 59