Composition of Fixed Maturities by Maturity (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012		Sep. 30, 2012
Schedule of Available-for-sale Securities [Line Items]
Open interest rate swap positions	$ 53.5	[1]	$ (95.5)	[1]	$ (101.3)	[1]
Interest rate swaps
Schedule of Available-for-sale Securities [Line Items]
Open interest rate swap positions	$ 53.5

[1] To the extent we hold both derivative assets and liabilities with the same counterparty that are subject to an enforceable master netting arrangement, we expect that we will report them on a gross basis on our balance sheets, consistent with our historical presentation.