Investments (Aggregate Fair Value And Gross Unrealized Loss By Length Of Time Security Has Continuously Been In Unrealized Loss Position) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Investment [Line Items]
Document Period End Date	Mar. 31, 2016
Fair Value, 0-12 Months	$ 12,795	$ 16,763
Gross Unrealized Loss, 0-12 Months	(287)	(601)
Fair Value, Over 12 Months	2,064	1,885
Gross Unrealized Loss, Over 12 Months	(138)	(226)
Total Fair Value	14,859	18,648
Total Gross Unrealized Loss	(425)	(827)
U.S. Treasury And Agency [Member]
Investment [Line Items]
Fair Value, 0-12 Months		996
Gross Unrealized Loss, 0-12 Months		(5)
Fair Value, Over 12 Months		153
Gross Unrealized Loss, Over 12 Months		(1)
Total Fair Value		1,149
Total Gross Unrealized Loss		(6)
Foreign [Member]
Investment [Line Items]
Fair Value, 0-12 Months	3,204	3,953
Gross Unrealized Loss, 0-12 Months	(69)	(148)
Fair Value, Over 12 Months	486	436
Gross Unrealized Loss, Over 12 Months	(53)	(73)
Total Fair Value	3,690	4,389
Total Gross Unrealized Loss	(122)	(221)
Corporate [Member]
Investment [Line Items]
Fair Value, 0-12 Months	4,014	7,518
Gross Unrealized Loss, 0-12 Months	(152)	(371)
Fair Value, Over 12 Months	651	738
Gross Unrealized Loss, Over 12 Months	(76)	(138)
Total Fair Value	4,665	8,256
Total Gross Unrealized Loss	(228)	(509)
Collateralized Mortgage Backed Securities [Member]
Investment [Line Items]
Fair Value, 0-12 Months	1,190	3,399
Gross Unrealized Loss, 0-12 Months	(4)	(42)
Fair Value, Over 12 Months	854	516
Gross Unrealized Loss, Over 12 Months	(7)	(12)
Total Fair Value	2,044	3,915
Total Gross Unrealized Loss	(11)	(54)
US States and Political Subdivisions Debt Securities [Member]
Investment [Line Items]
Fair Value, 0-12 Months	3,848	556
Gross Unrealized Loss, 0-12 Months	(12)	(6)
Fair Value, Over 12 Months	73	42
Gross Unrealized Loss, Over 12 Months	(2)	(2)
Total Fair Value	3,921	598
Total Gross Unrealized Loss	(14)	(8)
Fixed Maturities [Member]
Investment [Line Items]
Fair Value, 0-12 Months	12,256	16,422
Gross Unrealized Loss, 0-12 Months	(237)	(572)
Fair Value, Over 12 Months	2,064	1,885
Gross Unrealized Loss, Over 12 Months	(138)	(226)
Total Fair Value	14,320	18,307
Total Gross Unrealized Loss	(375)	(798)
Equity Securities [Member]
Investment [Line Items]
Fair Value, 0-12 Months	310	131
Gross Unrealized Loss, 0-12 Months	(32)	(18)
Fair Value, Over 12 Months	0	0
Gross Unrealized Loss, Over 12 Months	0	0
Total Fair Value	310	131
Total Gross Unrealized Loss	(32)	(18)
Other Long-term Investments [Member]
Investment [Line Items]
Fair Value, 0-12 Months	229	210
Gross Unrealized Loss, 0-12 Months	(18)	(11)
Fair Value, Over 12 Months	0	0
Gross Unrealized Loss, Over 12 Months	0	0
Total Fair Value	229	210
Total Gross Unrealized Loss	$ (18)	$ (11)