Commitments and Contingent Liabilities (Narrative) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014 credit_facilities	Dec. 31, 2013
Commitments And Contingent Liabilities [Line Items]
Undrawn outstanding letters of credit in favor of third parties	$ 195.4	$ 210.3
Undrawn outstanding letters of credit between subsidiaries	1,216.3	995.5
Number of credit facilities	9
Guarantee Of Subsidiary Collateral Financing [Member]
Commitments And Contingent Liabilities [Line Items]
Guarantor Obligations, Current Carrying Value	300.0
Credit Facility 850 Million [Member]
Commitments And Contingent Liabilities [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	850.0
Letter of Credit [Member]
Commitments And Contingent Liabilities [Line Items]
Number of credit facilities	8
Line of Credit Facility, Maximum Borrowing Capacity	$ 1,060.2