Unaudited Consolidated Quarterly Financial Data (Detail) (USD $) In Millions, except Per Share data, 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
Schedule of Condensed Consolidating Statement of Operations [Line Items]
Premium income	$ 5,643	$ 5,660	$ 5,467	$ 5,378	$ 5,324	$ 5,210	$ 4,956	$ 4,872	$ 22,148	$ 20,362	$ 18,073
Net investment income	876	869	845	882	858	843	784	794	3,473	3,280	3,007
Realized investment gains (losses)	(171)	286	(418)	(45)	(223)	(83)	(668)	(579)
Other income	27	32	8	25	20	17	16	30	92	81	74
Total revenues	6,375	6,847	5,902	6,240	5,979	5,987	5,088	5,117	25,364	22,171	20,732
Total benefits and expenses	5,495	5,367	5,161	5,038	5,157	4,895	4,644	4,526	21,062	19,221	17,171
Earnings before income taxes	880	1,480	741	1,202	822	1,092	444	591	4,302	2,950	3,561
Total income tax expense	299	463	258	417	284	356	170	202	1,436	1,013	1,233
Net earnings	$ 581	$ 1,017	$ 483	$ 785	$ 538	$ 736	$ 274	$ 389
Net earnings per basic share	$ 1.24	$ 2.17	$ 1.04	$ 1.68	$ 1.16	$ 1.58	$ 0.59	$ 0.83	$ 6.14	$ 4.16	$ 4.96
Net earnings per diluted share	$ 1.24	$ 2.16	$ 1.03	$ 1.68	$ 1.15	$ 1.57	$ 0.58	$ 0.83	$ 6.11	$ 4.12	$ 4.92