Leases - Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 116	$ 94
Operating cash flows from finance leases	16	3
Financing cash flows from finance leases	161	17
Right-of-use assets obtained in exchange for lease liabilities:
Operating leases	2	459
Finance leases	$ 331	$ 288