Accounts Receivable (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Accounts Receivable
Advance cash payments received from third parties to mitigate credit risk	$ 110	$ 180
Standby letters of credit	$ 46	$ 198
Substantially all trade accounts receivable, net, maximum age of balances past their scheduled invoice date	30 days	30 days
Allowance for doubtful accounts receivable	$ 4	$ 4