Statutory Net Income and Surplus (Detail) (U.S. Insurance Subsidiaries, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
U.S. Insurance Subsidiaries
Statutory Accounting Practices [Line Items]
Statutory Net Income (Loss)	$ (47.3)	$ (5.2)	$ 101.7
Statutory Surplus	$ 1,523.4	$ 1,582.8	$ 1,747.3