Investments - Net Investment Income and Investment Gains (Losses) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Net Investment Income [Line Items]
Total investment income	$ 661	$ 695	$ 1,907	$ 1,836
Investment expenses	(14)	(13)	(40)	(42)
Net investment income	647	682	1,867	1,794
Investment gains	4	7	14	59
Fixed maturity securities [Member]
Net Investment Income [Line Items]
Total investment income	504	507	1,501	1,528
Investment gains	7	26	34	73
Short term investments [Member]
Net Investment Income [Line Items]
Total investment income	2	3	5	10
Investment gains	1	(2)	2	4
Limited partnership investments [Member]
Net Investment Income [Line Items]
Total investment income	115	110	345	210
Equity securities [Member]
Net Investment Income [Line Items]
Total investment income	3	4	9	10
Investment gains	(2)	(15)	(17)	(14)
Income from trading portfolio [Member]
Net Investment Income [Line Items]
Total investment income	30	66	28	62
Other [Member]
Net Investment Income [Line Items]
Total investment income	7	5	19	16
Derivative instruments [Member]
Net Investment Income [Line Items]
Investment gains	$ (2)	$ (2)	$ (5)	$ (4)