Segment Information (Net Premiums Earned By Geographic Region) (Details)		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
North America [Member]
Segment Reporting Information [Line Items]
Percentage of net premiums earned by geographic region		70.00%	70.00%	70.00%
Europe [Member]
Segment Reporting Information [Line Items]
Percentage of net premiums earned by geographic region	[1]	11.00%	11.00%	12.00%
Asia Pacific and Far East [Member]
Segment Reporting Information [Line Items]
Percentage of net premiums earned by geographic region		12.00%	12.00%	11.00%
Latin America [Member]
Segment Reporting Information [Line Items]
Percentage of net premiums earned by geographic region		7.00%	7.00%	7.00%

[1] (1) Europe includes Eurasia and Africa regions.