Unaudited Consolidated Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Condensed Income Statements, [Line Items]
Net premium income	$ 4,653	$ 4,623	$ 4,664	$ 4,681	$ 4,671	$ 4,736	$ 4,681	$ 4,691	$ 18,622	$ 18,780	$ 18,677
Net investment income	968	896	870	904	886	936	878	878	3,638	3,578	3,442
Net investment gains (losses)	256	108	(170)	(463)	12	(153)	(66)	71	(270)	(135)	(430)
Other income (loss)	36	38	43	40	34	17	18	17	157	84	69
Total revenues	5,913	5,665	5,407	5,162	5,603	5,536	5,511	5,657	22,147	22,307	21,758
Total benefits and expenses	4,697	4,512	4,337	4,442	4,545	4,500	4,402	4,415	17,988	17,862	17,775
Earnings before income taxes	1,216	1,153	1,070	720	1,058	1,036	1,109	1,242	4,159	4,445	3,983
Total income tax expense	265	(1,303)	265	154	276	259	292	314	$ (619)	$ 1,141	$ 1,063
Net earnings	$ 951	$ 2,456	$ 805	$ 566	$ 782	$ 777	$ 817	$ 928
Net earnings per basic share	$ 1.36	$ 3.45	$ 1.12	$ 0.78	$ 1.07	$ 1.05	$ 1.10	$ 1.23	$ 6.69	$ 4.45	$ 3.79
Net earnings per diluted share	$ 1.35	$ 3.44	$ 1.12	$ 0.78	$ 1.06	$ 1.04	$ 1.09	$ 1.23	$ 6.67	$ 4.43	$ 3.77
Parent Company
Condensed Income Statements, [Line Items]
Net investment income									$ 62	$ 77	$ 69
Net investment gains (losses)									399	98	(16)
Total revenues									595	330	247
Total income tax expense									$ (15)	$ (22)	$ (12)