Commitments Contingencies and Guarantees (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Other Commitments [Line Items]
Undrawn Outstanding Letters Of Credit In Favor Of Third Parties	$ 132,200,000	$ 176,500,000
Undrawn Outstanding Letters Of Credit Between Subsidiaries	1,127,400,000	1,035,000,000
Line of Credit Facility, Maximum Borrowing Capacity	701,100,000.0
Line of Credit Facility, Commitment Fee Amount	10,900,000	12,600,000	$ 9,800,000
Operating Leases, Rent Expense	12,100,000	19,300,000	$ 18,500,000
Maximum Capital Lease Obligations As Offset Against Industrial Bonds	150,000,000
Insurance Treaty Guarantee Net Of Assets Held In Trust [Member]
Other Commitments [Line Items]
Guarantor Obligations, Current Carrying Value	634,909,000,000	664,913,000,000
Guarantee Of Borrowed Securities [Member]
Other Commitments [Line Items]
Guarantor Obligations, Current Carrying Value	259,540,000,000	$ 201,050,000,000
Syndicated Credit Facility $850 Million [Member]
Other Commitments [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 850,000,000