Fair Value Measurements (Narrative) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
Jun. 30, 2011
Fair value interest rate swap discount rate	1.60%
Assets transferred between level 1 and level 2	0
Senior Debt Obligations Due 2014 [Member]
Fair value interest rate swap derivatives	$ 250
Debt instrument, maturity date	Dec. 31, 2014

Fair value as of the balance sheet date of interest rate derivative assets, net of interest rate derivative liabilities, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized on the balance sheet.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 107
-Paragraph 10
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6947722&loc=d3e13433-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=6947722&loc=d3e13495-108611

Name:	us-gaap_InterestRateDerivativesAtFairValueNet
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant