Segment Information (Broker details) (Details)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Economic Dependence [Line Items]
Cedant Percentage Of Gross Written Premium	5.00%	5.00%	5.00%
North America Segment [Member]
Economic Dependence [Line Items]
Broker Percentage Of Gross Written Premium	60.00%	70.00%	64.00%
Global (Non-US) P&C [Member]
Economic Dependence [Line Items]
Broker Percentage Of Gross Written Premium	29.00%	28.00%	29.00%
Global Specialty [Member]
Economic Dependence [Line Items]
Broker Percentage Of Gross Written Premium	41.00%	42.00%	43.00%
Catastrophe Segment [Member]
Economic Dependence [Line Items]
Broker Percentage Of Gross Written Premium	74.00%	74.00%	81.00%
Life and Health [Member]
Economic Dependence [Line Items]
Broker Percentage Of Gross Written Premium	12.00%	13.00%	16.00%
Broker A [Member]
Economic Dependence [Line Items]
Broker Percentage Of Gross Written Premium	22.00%	24.00%	26.00%
Broker B [Member]
Economic Dependence [Line Items]
Broker Percentage Of Gross Written Premium	21.00%	22.00%	21.00%