Investments (Aggregate Fair Value And Gross Unrealized Loss By Length Of Time Security Has Continuously Been In Unrealized Loss Position) (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Investment [Line Items]
Document Period End Date	Sep. 30, 2015
Fair Value, 0-12 Months	$ 13,641	$ 8,559
Gross Unrealized Loss, 0-12 Months	(532)	(244)
Fair Value, Over 12 Months	1,945	3,932
Gross Unrealized Loss, Over 12 Months	(148)	(79)
Total Fair Value	15,586	12,491
Total Gross Unrealized Loss	(680)	(323)
U.S. Treasury And Agency [Member]
Investment [Line Items]
Fair Value, 0-12 Months	228	350
Gross Unrealized Loss, 0-12 Months	(1)	(1)
Fair Value, Over 12 Months	59	666
Gross Unrealized Loss, Over 12 Months	0	(9)
Total Fair Value	287	1,016
Total Gross Unrealized Loss	(1)	(10)
Foreign [Member]
Investment [Line Items]
Fair Value, 0-12 Months	3,627	2,262
Gross Unrealized Loss, 0-12 Months	(160)	(75)
Fair Value, Over 12 Months	402	375
Gross Unrealized Loss, Over 12 Months	(52)	(15)
Total Fair Value	4,029	2,637
Total Gross Unrealized Loss	(212)	(90)
Corporate Securities [Member]
Investment [Line Items]
Fair Value, 0-12 Months	6,641	4,684
Gross Unrealized Loss, 0-12 Months	(322)	(150)
Fair Value, Over 12 Months	801	738
Gross Unrealized Loss, Over 12 Months	(84)	(22)
Total Fair Value	7,442	5,422
Total Gross Unrealized Loss	(406)	(172)
Collateralized Mortgage Backed Securities [Member]
Investment [Line Items]
Fair Value, 0-12 Months	2,145	704
Gross Unrealized Loss, 0-12 Months	(16)	(2)
Fair Value, Over 12 Months	626	1,663
Gross Unrealized Loss, Over 12 Months	(10)	(28)
Total Fair Value	2,771	2,367
Total Gross Unrealized Loss	(26)	(30)
US States and Political Subdivisions Debt Securities [Member]
Investment [Line Items]
Fair Value, 0-12 Months	766	458
Gross Unrealized Loss, 0-12 Months	(7)	(3)
Fair Value, Over 12 Months	57	490
Gross Unrealized Loss, Over 12 Months	(2)	(5)
Total Fair Value	823	948
Total Gross Unrealized Loss	(9)	(8)
Fixed Maturities [Member]
Investment [Line Items]
Fair Value, 0-12 Months	13,407	8,458
Gross Unrealized Loss, 0-12 Months	(506)	(231)
Fair Value, Over 12 Months	1,945	3,932
Gross Unrealized Loss, Over 12 Months	(148)	(79)
Total Fair Value	15,352	12,390
Total Gross Unrealized Loss	(654)	(310)
Equity Securities [Member]
Investment [Line Items]
Fair Value, 0-12 Months	151	101
Gross Unrealized Loss, 0-12 Months	(24)	(13)
Fair Value, Over 12 Months	0	0
Gross Unrealized Loss, Over 12 Months	0	0
Total Fair Value	151	101
Total Gross Unrealized Loss	(24)	$ (13)
Other Long-term Investments [Member]
Investment [Line Items]
Fair Value, 0-12 Months	83
Gross Unrealized Loss, 0-12 Months	(2)
Fair Value, Over 12 Months	0
Gross Unrealized Loss, Over 12 Months	0
Total Fair Value	83
Total Gross Unrealized Loss	$ (2)