Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Statement Of Financial Position [Abstract]
Allowance for doubtful accounts receivable	$ 83	$ 78
Allowance for doubtful notes receivable	$ 2	$ 2
Common stock, par value	$ 0.01	$ 0.01
Common stock, authorized	1,000,000,000	1,000,000,000
Common stock, outstanding	169,537,501	168,754,605