Accounts Receivable (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Accounts Receivable [Abstract]
Bad debt expense	$ 20	$ 17	$ 46	$ 41