Unaudited Consolidated Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Income Statements, [Line Items]
Net premium income	$ 4,671	$ 4,736	$ 4,681	$ 4,691	$ 4,591	$ 4,636	$ 4,706	$ 4,745	$ 18,780	$ 18,677	$ 18,531
Net investment income	886	936	878	878	874	870	862	837	3,578	3,442	3,220
Realized investment gains (losses)	12	(153)	(66)	71	(355)	56	3	(134)
Other income (loss)	34	17	18	17	16	15	18	16	84	69	67
Total revenues	5,603	5,536	5,511	5,657	5,126	5,577	5,589	5,464	22,307	21,758	21,667
Total benefits and expenses	4,545	4,500	4,402	4,415	4,404	4,431	4,458	4,482	17,862	17,775	17,649
Earnings before income taxes	1,058	1,036	1,109	1,242	722	1,146	1,131	982	4,445	3,983	4,018
Total income tax expense	276	259	292	314	197	301	299	265	$ 1,141	$ 1,063	$ (586)
Net earnings	$ 782	$ 777	$ 817	$ 928	$ 525	$ 845	$ 832	$ 717
Net earnings per basic share	$ 1.07	$ 1.05	$ 1.10	$ 1.23	$ 0.69	$ 1.10	$ 1.08	$ 0.92	$ 4.45	$ 3.79	$ 5.81
Net earnings per diluted share	$ 1.06	$ 1.04	$ 1.09	$ 1.23	$ 0.69	$ 1.09	$ 1.07	$ 0.91	$ 4.43	$ 3.77	$ 5.77
Parent Company
Condensed Income Statements, [Line Items]
Net investment income									$ 77	$ 69	$ 30
Total revenues									330	247	331
Total income tax expense									$ (22)	$ (12)	$ (23)