Leases (Supplemental Cash Flow Information Related To Leases) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Operating cash flows provided by operating leases	$ 67	$ 70
Operating cash flows used by operating leases	(68)	(76)
Operating cash flows used by finance leases	(13)	(15)
Financing cash flows used by finance leases	(23)	(35)	$ (36)
Right-of-use assets obtained in exchange for lease liabilities, Operating leases	28	42
Right-of-use assets obtained in exchange for lease liabilities, Finance leases	$ 3	$ 34