Consolidated Statements of Cash Flows (Unaudited) (Parenthetical) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Statement Of Cash Flows [Abstract]
Financing leases	$ 42	$ 98
Operating leases	$ 3	$ 4
Supplemental line of credit facility borrowings expiration period	364 days