Debt and Equity Securities (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Investments Debt And Equity Securities [Abstract]
Realized gains on sales of securities	$ 1.3	$ 9.9	$ 6.5	$ 24.6
Realized losses on sales of securities	$ 1.6	$ 1.7	$ 8.2	$ 6.1