Leases - Supplemental lease cash flow information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 43	$ 30
Reduction of gain on sale leaseback	1	(136)	$ (33)
Right-of-use assets obtained in exchange for lease obligations:
Operating leases	$ 16	$ 72