Investments (Aggregate Fair Value And Gross Unrealized Loss By Length Of Time Security Has Continuously Been In Unrealized Loss Position) (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Investment [Line Items]
Investment securities, Unrealized loss position, 0-12 Months, Fair Value	$ 5,198	$ 3,968
Investment securities, Unrealized loss position, 0-12 Months, Gross Unrealized Loss	(65)	(48)
Investment securities, Unrealized loss position, Over 12 Months, Fair Value	324	577
Investment securities, Unrealized loss position, Over 12 Months, Gross Unrealized Loss	(26)	(50)
Investment securities, Unrealized loss position, Total Fair Value	5,522	4,545
Investment securities, Unrealized loss position, Total Gross Unrealized Loss	(91)	(98)
US Treasury and Government [Member]
Investment [Line Items]
Investment securities, Unrealized loss position, 0-12 Months, Fair Value	576	440
Investment securities, Unrealized loss position, 0-12 Months, Gross Unrealized Loss	(5)	(1)
Investment securities, Unrealized loss position, Over 12 Months, Fair Value	0	0
Investment securities, Unrealized loss position, Over 12 Months, Gross Unrealized Loss	0	0
Investment securities, Unrealized loss position, Total Fair Value	576	440
Investment securities, Unrealized loss position, Total Gross Unrealized Loss	(5)	(1)
Foreign Government Debt Securities [Member]
Investment [Line Items]
Investment securities, Unrealized loss position, 0-12 Months, Fair Value	723	1,234
Investment securities, Unrealized loss position, 0-12 Months, Gross Unrealized Loss	(11)	(8)
Investment securities, Unrealized loss position, Over 12 Months, Fair Value	69	88
Investment securities, Unrealized loss position, Over 12 Months, Gross Unrealized Loss	(5)	(6)
Investment securities, Unrealized loss position, Total Fair Value	792	1,322
Investment securities, Unrealized loss position, Total Gross Unrealized Loss	(16)	(14)
Corporate Securities [Member]
Investment [Line Items]
Investment securities, Unrealized loss position, 0-12 Months, Fair Value	1,163	1,026
Investment securities, Unrealized loss position, 0-12 Months, Gross Unrealized Loss	(21)	(23)
Investment securities, Unrealized loss position, Over 12 Months, Fair Value	78	85
Investment securities, Unrealized loss position, Over 12 Months, Gross Unrealized Loss	(7)	(8)
Investment securities, Unrealized loss position, Total Fair Value	1,241	1,111
Investment securities, Unrealized loss position, Total Gross Unrealized Loss	(28)	(31)
Collateralized Mortgage Backed Securities [Member]
Investment [Line Items]
Investment securities, Unrealized loss position, 0-12 Months, Fair Value	1,943	855
Investment securities, Unrealized loss position, 0-12 Months, Gross Unrealized Loss	(15)	(4)
Investment securities, Unrealized loss position, Over 12 Months, Fair Value	140	356
Investment securities, Unrealized loss position, Over 12 Months, Gross Unrealized Loss	(11)	(32)
Investment securities, Unrealized loss position, Total Fair Value	2,083	1,211
Investment securities, Unrealized loss position, Total Gross Unrealized Loss	(26)	(36)
US States and Political Subdivisions Debt Securities [Member]
Investment [Line Items]
Investment securities, Unrealized loss position, 0-12 Months, Fair Value	742	316
Investment securities, Unrealized loss position, 0-12 Months, Gross Unrealized Loss	(6)	(3)
Investment securities, Unrealized loss position, Over 12 Months, Fair Value	37	48
Investment securities, Unrealized loss position, Over 12 Months, Gross Unrealized Loss	(3)	(4)
Investment securities, Unrealized loss position, Total Fair Value	779	364
Investment securities, Unrealized loss position, Total Gross Unrealized Loss	(9)	(7)
Fixed Maturities [Member]
Investment [Line Items]
Investment securities, Unrealized loss position, 0-12 Months, Fair Value	5,147	3,871
Investment securities, Unrealized loss position, 0-12 Months, Gross Unrealized Loss	(58)	(39)
Investment securities, Unrealized loss position, Over 12 Months, Fair Value	324	577
Investment securities, Unrealized loss position, Over 12 Months, Gross Unrealized Loss	(26)	(50)
Investment securities, Unrealized loss position, Total Fair Value	5,471	4,448
Investment securities, Unrealized loss position, Total Gross Unrealized Loss	(84)	(89)
Equity Securities [Member]
Investment [Line Items]
Investment securities, Unrealized loss position, 0-12 Months, Fair Value	47	29
Investment securities, Unrealized loss position, 0-12 Months, Gross Unrealized Loss	(4)	(4)
Investment securities, Unrealized loss position, Over 12 Months, Fair Value	0	0
Investment securities, Unrealized loss position, Over 12 Months, Gross Unrealized Loss	0	0
Investment securities, Unrealized loss position, Total Fair Value	47	29
Investment securities, Unrealized loss position, Total Gross Unrealized Loss	(4)	(4)
Other Long-term Investments [Member]
Investment [Line Items]
Investment securities, Unrealized loss position, 0-12 Months, Fair Value	4	68
Investment securities, Unrealized loss position, 0-12 Months, Gross Unrealized Loss	(3)	(5)
Investment securities, Unrealized loss position, Over 12 Months, Fair Value	0	0
Investment securities, Unrealized loss position, Over 12 Months, Gross Unrealized Loss	0	0
Investment securities, Unrealized loss position, Total Fair Value	4	68
Investment securities, Unrealized loss position, Total Gross Unrealized Loss	$ (3)	$ (5)