Fair Value Measurements (Narrative) (Details) (USD $)	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010
Fair Value Measurements
Net assets measured at fair value on a recurring basis	$ 1,700,000,000	$ 1,600,000,000
Net assets measured at fair value on a recurring basis measured using unobservable inputs	(3,000,000)	190,000,000
Level 3 net assets as a percentage of total assets	1.00%	1.00%
Assets transferred from Level 3 to Level 2	$ 8,000,000

Transfers out of assets measured at fair value and categorized within Level 3 of the fair value hierarchy that have taken place during the period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19207-110258

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration