Unaudited Consolidated Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Income Statements, [Line Items]
Net premium income	$ 4,778	$ 5,022	$ 4,823	$ 4,602	$ 4,394	$ 4,380	$ 4,364	$ 4,432	$ 19,225	$ 17,570	$ 19,072
Net investment income	813	842	822	801	792	784	777	782	3,278	3,135	3,319
Realized investment gains (losses)	137	(146)	(187)	73	114	(114)	127	13
Other income (loss)	227	(2)	(21)	(25)	19	(10)	19	(1)	179	27	122
Total revenues	5,955	5,716	5,437	5,451	5,319	5,040	5,287	5,226	22,559	20,872	22,728
Total benefits and expenses	4,802	4,753	4,603	4,334	4,209	4,176	4,413	4,213	18,492	17,010	18,237
Earnings before income taxes	1,153	963	834	1,117	1,110	864	874	1,013	4,067	3,862	4,491
Total income tax expense	402	334	286	386	380	297	301	350	$ 1,408	$ 1,329	$ 1,540
Net earnings	$ 751	$ 629	$ 548	$ 731	$ 730	$ 567	$ 573	$ 663
Net earnings per basic share	$ 1.85	$ 1.54	$ 1.33	$ 1.75	$ 1.72	$ 1.32	$ 1.33	$ 1.52	$ 6.46	$ 5.88	$ 6.54
Net earnings per diluted share	$ 1.84	$ 1.53	$ 1.32	$ 1.74	$ 1.71	$ 1.32	$ 1.32	$ 1.51	$ 6.42	$ 5.85	$ 6.50
Parent Company
Condensed Income Statements, [Line Items]
Net investment income									$ 18	$ 22	$ 13
Other income (loss)									0	0	(11)
Total revenues									2,233	2,714	2,122
Earnings before income taxes									1,743	2,162	1,791
Total income tax expense									$ (102)	$ (80)	$ 121
Yen Denominated Loan Three Point Zero Zero Percent Due August Twenty Fifteen [Member] | Parent Company
Condensed Income Statements, [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	0.46%								0.46%