Unaudited Consolidated Quarterly Financial Data (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Schedule of Condensed Consolidating Statement of Operations [Line Items]
Premium income	$ 5,324	$ 5,210	$ 4,956	$ 4,872	$ 4,785	$ 4,607	$ 4,333	$ 4,348	$ 20,362	$ 18,073	$ 16,621
Net Investment Income	858	843	784	794	789	765	727	726	3,280	3,007	2,765
Realized investment gains (losses)	(223)	(83)	(668)	(579)	(295)	9	(89)	(46)
Other income	20	17	16	30	15	13	9	37	81	74	80
Total revenues	5,979	5,987	5,088	5,117	5,294	5,394	4,980	5,065	22,171	20,732	18,254
Total benefits and expenses	5,145	4,882	4,635	4,517	4,627	4,339	4,091	4,091	19,179	17,147	16,019
Earnings before income taxes	834	1,105	453	600	667	1,055	889	974	2,992	3,585	2,235
Total income tax	288	361	173	205	230	365	308	338	(1,028)	(1,241)	(738)
Net earnings	$ 546	$ 744	$ 280	$ 395	$ 437	$ 690	$ 581	$ 636
Net earnings per basic share	$ 1.17	$ 1.60	$ 0.60	$ 0.84	$ 0.93	$ 1.47	$ 1.24	$ 1.36	$ 4.21	$ 5.00	$ 3.21
Net earnings per diluted share	$ 1.17	$ 1.59	$ 0.60	$ 0.84	$ 0.92	$ 1.46	$ 1.23	$ 1.35	$ 4.18	$ 4.95	$ 3.19