Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Statement Of Financial Position [Abstract]
Allowance for doubtful accounts receivable	$ 85	$ 63
Allowance for doubtful notes receivable	$ 3	$ 4
Common stock, par value	$ 0.01	$ 0.01
Common stock, authorized	1,000,000,000	1,000,000,000
Common stock, outstanding	169,307,152	172,694,299