Investments in fixed maturity securities - Narrative (Detail) (USD $) In Millions	9 Months Ended
	Sep. 30, 2011 Insurance and Other [Member]	Sep. 30, 2011 Fixed Maturities [Member]	Dec. 31, 2010 Fixed Maturities [Member]
Investments in securities with fixed maturities [Line Items]
Term over which certain securities were in an unrealized loss position	more than 12 months
Unrealized losses related to securities that have been in an unrealized loss position for more than 12 months		$ 16	$ 24