Unaudited Consolidated Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Income Statements, [Line Items]
Net investment income	$ 792	$ 784	$ 777	$ 782	$ 808	$ 841	$ 843	$ 827	$ 3,135	$ 3,319	$ 3,293
Net premium income	4,394	4,380	4,364	4,432	4,489	4,841	4,888	4,854	17,570	19,072	20,135
Realized investment gains (losses)	114	(114)	127	13	143	16	102	(46)
Other income (loss)	19	(10)	19	(1)	74	38	5	5	27	122	112
Total revenues	5,319	5,040	5,287	5,226	5,514	5,736	5,838	5,640	20,872	22,728	23,939
Total benefits and expenses	4,209	4,176	4,413	4,213	4,439	4,662	4,600	4,536	17,010	18,237	19,123
Earnings before income taxes	1,110	864	874	1,013	1,075	1,074	1,238	1,104	3,862	4,491	4,816
Total income tax expense	380	297	301	350	372	368	428	372	$ 1,329	$ 1,540	$ 1,658
Net earnings	$ 730	$ 567	$ 573	$ 663	$ 703	$ 706	$ 810	$ 732
Net earnings per basic share	$ 1.72	$ 1.32	$ 1.33	$ 1.52	$ 1.57	$ 1.56	$ 1.79	$ 1.61	$ 5.88	$ 6.54	$ 6.80
Net earnings per diluted share	$ 1.71	$ 1.32	$ 1.32	$ 1.51	$ 1.57	$ 1.56	$ 1.78	$ 1.60	$ 5.85	$ 6.50	$ 6.76