Changes in Level 3 Assets (Detail) (Auction Rate Securities, USD $) In Millions, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013	Jun. 30, 2014		Jun. 30, 2013
Auction Rate Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Assets Beginning Balance	$ 98.5		$ 99.6	$ 98.9		$ 97.8
Total Gains (Losses):
Included in Earnings						0.1	[1]
Included in Other Comprehensive Income	0.5	[2]		0.3	[2]	2.7	[2]
Purchases, Issuances, Sales, and Settlements
Sales				0.1
Settlements				(0.5)		(1.5)
Purchases, Issuances, Sales, and Settlements	(0.2)		(0.5)
Fair Value Assets Ending Balance	$ 98.8		$ 99.1	$ 98.8		$ 99.1

[1] Realized gains for the six month period ended June 30, 2013 of $0.1 million represent gains from redemptions by issuers, which are recorded in interest income within the consolidated statement of income.

[2] Unrealized gains (losses) are included in net unrealized gains (losses) on securities available for sale within the consolidated statement of comprehensive income.