Marketable Securities (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Investments in marketable securities
Marketable securities, amortized cost	$ 138	$ 131
Marketable securities, fair value	138	131
Corporate debt securities [Member]
Investments in marketable securities
Marketable securities, amortized cost	88	82
Marketable securities, fair value	88	82
U.S. government and agency debt securities [Member]
Investments in marketable securities
Marketable securities, amortized cost	11	16
Marketable securities, fair value	11	16
Non-U.S. government debt securities [Member]
Investments in marketable securities
Marketable securities, amortized cost	0	1
Marketable securities, fair value	0	1
Asset-backed debt securities [Member]
Investments in marketable securities
Marketable securities, amortized cost	14	6
Marketable securities, fair value	14	6
Certificates of deposit [Member]
Investments in marketable securities
Marketable securities, amortized cost	17	16
Marketable securities, fair value	17	16
Municipal debt securities [Member]
Investments in marketable securities
Marketable securities, amortized cost	8	10
Marketable securities, fair value	$ 8	$ 10