Investments (Schedule Of Net Investment Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Net Investment Income [Line Items]
Net investment income	$ 52.3	$ 53.3
Fixed maturity investments
Net Investment Income [Line Items]
Net investment income	44.9	48.0
Equity securities
Net Investment Income [Line Items]
Net investment income	2.9	1.8
Other invested assets: hedge funds and private equity
Net Investment Income [Line Items]
Net investment income	7.0	4.7
Other invested assets: other private securities
Net Investment Income [Line Items]
Net investment income	1.0	3.1
Cash and cash equivalents
Net Investment Income [Line Items]
Net investment income	0.9	0.5
Expenses
Net Investment Income [Line Items]
Net investment income	$ (4.4)	$ (4.8)