Marketable Securities (Details) (USD $) In Millions	Jun. 30, 2011
Investments in marketable securities
Marketable securities, amortized cost	$ 323
Marketable securities	323
Corporate debt securities [Member]
Investments in marketable securities
Marketable securities, amortized cost	167
Marketable securities	167
U.S. government and agency debt securities [Member]
Investments in marketable securities
Marketable securities, amortized cost	63
Marketable securities	63
Asset-backed debt securities [Member]
Investments in marketable securities
Marketable securities, amortized cost	18
Marketable securities	18
Certificates of deposit [Member]
Investments in marketable securities
Marketable securities, amortized cost	49
Marketable securities	49
Municipal debt securities [Member]
Investments in marketable securities
Marketable securities, amortized cost	26
Marketable securities	$ 26