Leases - Activities Associated With Operating Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Fixed lease expenses	$ 35	$ 37
Variable lease expenses	34	29
Total lease expenses	69	66
Cash paid for leases	69	67
ROU assets obtained in exchange for lease obligations	55	42
Reductions of ROU assets and lease liabilities	(3)	(16)
Net non-cash increases to ROU assets and lease liabilities	$ 52	$ 26