Acquisitions (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended			6 Months Ended		3 Months Ended	6 Months Ended	3 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Mar. 31, 2010	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011 Business Acquisition [Member]	Jun. 30, 2011 Business Acquisition [Member]	Mar. 31, 2010 Purchase Consideration for Acquisitions During the Period [Member]	Jun. 30, 2011 Purchase Consideration for Acquisitions During the Period [Member]	Mar. 31, 2011 Purchase Consideration for Acquisitions During the Period [Member]	Mar. 31, 2011 Prior Years Acquisitions [Member]	Dec. 31, 2010 Prior Years Acquisitions [Member]	Mar. 31, 2010 Prior Years Acquisitions [Member]
Total purchase consideration	$ 114	$ 472		$ 114	$ 472				$ 8	$ 114
Decrease in additional paid in capital	2			2
Cash	101			101				239	101
Contingent consideration	13			13				55	13			2
Deferred purchase consideration	15			15							13	14	15
Number of acquisitions made			2
Issuance of shares								7.4
Fair value								178
Revenue target period, in years					two to four years
Revenue related to acquisitions	2,930	2,655		5,818	5,413	17	34
Net operating income related to acquisitions	$ 287	$ (27)		$ 606	$ 252	$ 3	$ 6