Investments (Net Investment Income) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income before expenses and fees	$ 867	$ 905	$ 1,722	$ 1,760
Expenses and fees	(21)	(24)	(44)	(49)
Net investment income	846	881	1,678	1,711
Fixed maturity securities - taxable
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income before expenses and fees	669	693	1,329	1,363
Fixed maturity securities - non-taxable
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income before expenses and fees	3	10	7	21
Commercial mortgage loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income before expenses and fees	85	92	169	184
Restricted Commercial Mortgage Loans Related to Securitization Entities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income before expenses and fees	7	9	16	19
Equity securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income before expenses and fees	6	10	10	13
Other Invested Assets
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income before expenses and fees	56	55	109	89
Policy loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income before expenses and fees	31	30	62	59
Cash, Cash Equivalents and Short-Term Investments
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income before expenses and fees	$ 10	$ 6	$ 20	$ 12