Commitments (Other Commitments Narrative) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011
Commitments
Construction commitments	$ 41.6
Letters of credit	$ 59.9

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

No definition available.

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant