Segment Information (Net Premiums Earned By Geographic Region) (Details)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting Information [Line Items]
Net Premiums Earned by Geographic Region	Years Ended
North America
Segment Reporting Information [Line Items]
Percentage of net premiums earned by geographic region	60.00%	61.00%	61.00%
Europe
Segment Reporting Information [Line Items]
Percentage of net premiums earned by geographic region	17.00%	18.00%	20.00%
Asia Pacific / Far East
Segment Reporting Information [Line Items]
Percentage of net premiums earned by geographic region	16.00%	14.00%	13.00%
Latin America
Segment Reporting Information [Line Items]
Percentage of net premiums earned by geographic region	7.00%	7.00%	6.00%