Fair Value Measurements (Narrative) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Credit-risk-related contingent features	we have no credit-risk-related contingent features in our agreements with the financial institutions that would require us to post collateral for derivative positions in a liability position.
SeniorNotesTotal [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes, fair value	$ 784.5
Senior notes, face value	$ 800.0