Fair Value Summary of Changes in Fair Value Associated With Level 3 Assets (Parenthetical) (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Net realized gains (losses) on securities	$ 40,400,000	$ 134,500,000	$ 159,800,000	$ 215,300,000
Equity securities | Nonredeemable preferred stocks | Hybrid Securities | Financials
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Net realized gains (losses) on securities	$ 1,700,000	$ 1,000,000	$ 4,800,000	$ 2,900,000