Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Allowance for doubtful accounts receivable	$ 20	$ 21
Assets, variable interest entity	3,134	3,079
Liabilities, variable interest entity	$ 2,760	$ 2,509
Preferred Stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred Stock, shares authorized	300,000,000	300,000,000
Preferred Stock, shares issued	0	0
Preferred Stock, shares outstanding	0	0
Common Stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common Stock, shares authorized (in shares)	3,000,000,000	3,000,000,000
Common Stock, shares issued (in shares)	85,205,012	85,535,501
Common Stock, shares outstanding (in shares)	85,205,012	85,535,501
Variable Interest Entities
Assets, variable interest entity	$ 800	$ 748
Liabilities, variable interest entity	$ 771	$ 750