Commitments, Contingencies and Other Items (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2011	Dec. 31, 2010	Dec. 31, 2005 claims
Commitments and Contingencies Disclosure [Abstract]
Number of purported state class actions			2
Amount outstanding under letters of credit	$ 22	$ 22

The total amount of pending claims pertaining to a loss contingency accrual as of the balance sheet date.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 5

-Paragraph 9, 10, 11, 12

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Name:	us-gaap_LossContingencyPendingClaimsNumber
Namespace Prefix:	us-gaap
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant