Marketable Securities (Contractual maturity) (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Marketable securities by contractual maturity
Due in one year or less	$ 71
Due after one year through five years	78
Due after five years through ten years	2
Due after ten years	15
Total marketable securities	$ 166	$ 1,454