Fair Value Measurements (Financial Instruments Measured At Fair Value On Recurring Basis) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	$ 46,504		$ 41,967
Equity securities, at fair value	770		647
Short-term investments	2,429		2,301
Other investments	2,621		2,314
Securities lending collateral	2,039		1,375
Investment derivative instruments	(3)		10
Other derivative instruments	38		41
Separate account assets	1,085		660
Total assets measured at fair value	55,483		49,315
GLB	1,279	[1]	1,319	[1]
U.S. Treasury And Agency [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	3,554		2,960
Foreign [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	13,967		12,401
Corporate Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	15,833		14,693
Mortgage Backed-Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	10,736		10,201
States, Municipalities, And Political Subdivisions [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	2,414		1,712
Fair Value, Inputs, Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	2,214		1,923
Equity securities, at fair value	761		632
Short-term investments	1,561		1,246
Other investments	248		208
Investment derivative instruments	(3)		10
Other derivative instruments	6		(16)
Separate account assets	1,024		607
Total assets measured at fair value	5,811		4,610
Fair Value, Inputs, Level 1 [Member] | U.S. Treasury And Agency [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	1,991		1,691
Fair Value, Inputs, Level 1 [Member] | Foreign [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	204		212
Fair Value, Inputs, Level 1 [Member] | Corporate Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	19		20
Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	44,105		39,843
Equity securities, at fair value	5		2
Short-term investments	868		1,055
Other investments	195		229
Securities lending collateral	2,039		1,375
Other derivative instruments	32		54
Separate account assets	61		53
Total assets measured at fair value	47,305		42,611
Fair Value, Inputs, Level 2 [Member] | U.S. Treasury And Agency [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	1,563		1,264
Fair Value, Inputs, Level 2 [Member] | Foreign [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	13,738		12,156
Fair Value, Inputs, Level 2 [Member] | Corporate Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	15,684		14,539
Fair Value, Inputs, Level 2 [Member] | Mortgage Backed-Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	10,707		10,173
Fair Value, Inputs, Level 2 [Member] | States, Municipalities, And Political Subdivisions [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	2,413		1,711
Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	185		201
Equity securities, at fair value	4		13
Other investments	2,178		1,877
Other derivative instruments	0		3
Total assets measured at fair value	2,367		2,094
GLB	1,279	[1]	1,319	[1]
Fair Value, Inputs, Level 3 [Member] | U.S. Treasury And Agency [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	0		5
Fair Value, Inputs, Level 3 [Member] | Foreign [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	25		33
Fair Value, Inputs, Level 3 [Member] | Corporate Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	130		134
Fair Value, Inputs, Level 3 [Member] | Mortgage Backed-Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	29		28
Fair Value, Inputs, Level 3 [Member] | States, Municipalities, And Political Subdivisions [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	$ 1		$ 1

[1] Our GLB reinsurance product meets the definition of a derivative instrument for accounting purposes and is accordingly carried at fair value. Excluded from the table above is the portion of the GLB derivative liability classified as Future policy benefits in the consolidated balance sheets. Refer to Note 5 for additional information.