Condensed Financial Information of Parent Company - Statements Of Income (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended									12 Months Ended
	Dec. 31, 2012		Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Revenues
Investment Income										$ 1,556	$ 1,644	$ 1,665
Other Revenues										8	9	13
Realized Investment Gains (Losses), Net										193	288	426
TOTAL REVENUES	3,400	[1]	3,362	3,423	3,410	3,345	3,420	3,400	3,420	13,595	13,585	13,319
Expenses
Corporate Expenses										270	287	290
Investment Expenses										38	39	35
Other Expenses										11	11	15
Federal and foreign income tax (credit)	(39)		194	123	173	150	68	127	176	451	521	814
NET INCOME	102	[1]	533	404	506	452	298	419	509	1,545	1,678	2,174
Other Comprehensive Income, Net of Tax										236	405	70
COMPREHENSIVE INCOME										1,781	2,083	2,244
Parent Company [Member]
Revenues
Investment Income										38	46	76
Other Revenues												2
Realized Investment Gains (Losses), Net										(6)	9	16
TOTAL REVENUES										32	55	94
Expenses
Corporate Expenses										268	285	288
Investment Expenses										2	3	3
Other Expenses												3
TOTAL EXPENSES										270	288	294
Loss before Federal and Foreign Income Tax and Equity in Net Income of Consolidated Subsidiaries										(238)	(233)	(200)
Federal and foreign income tax (credit)										4	1	(3)
Loss before Equity in Net Income of Consolidated Subsidiaries										(242)	(234)	(197)
Equity in Net Income of Consolidated Subsidiaries										1,787	1,912	2,371
NET INCOME										1,545	1,678	2,174
Other Comprehensive Income, Net of Tax										236	405	70
COMPREHENSIVE INCOME										$ 1,781	$ 2,083	$ 2,244

[1] In the fourth quarter of 2012, revenues were reduced by net reinsurance reinstatement premium costs of $53 million and losses and expenses included net losses of $829 million related to Storm Sandy. Net income for the quarter was reduced by $573 million or $2.15 per diluted share ($2.16 per share basic) for the after-tax effect of the net costs. Excluding the impact of Storm Sandy, the losses to premiums earned ratio was 50.9%, the expenses to premiums written ratio was 30.4% and the combined ratio was 81.3%.