Fair Value Measurements (Financial Instruments Measured At Fair Value On Recurring Basis) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	$ 47,306		$ 41,967
Equity securities	744		647
Short-term investments	2,228		2,301
Other investments	2,716		2,314
Securities lending collateral	1,791		1,375
Level 1
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	2,292		1,923
Equity securities	253		215
Short-term investments	1,503		1,246
Other investments	268		208
Securities lending collateral
Investment derivative instruments	11		10
Other derivative instruments	(6)		(16)
Separate account assets	872		607
Total assets measured at fair value	5,193		4,193
GLB		[1]		[1]
Level 1 | U.S. Treasury and agency
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	2,050		1,691
Level 1 | Foreign
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	222		212
Level 1 | Corporate securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	20		20
Level 1 | Mortgage backed-securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value
Level 1 | States, municipalities, and political subdivisions
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value
Level 2
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	44,839		39,843
Equity securities	488		419
Short-term investments	725		1,055
Other investments	196		229
Securities lending collateral	1,791		1,375
Investment derivative instruments
Other derivative instruments	30		54
Separate account assets	71		53
Total assets measured at fair value	48,140		43,028
GLB		[1]		[1]
Level 2 | U.S. Treasury and agency
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	1,685		1,264
Level 2 | Foreign
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	13,431		12,156
Level 2 | Corporate securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	16,586		14,539
Level 2 | Mortgage backed-securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	10,460		10,173
Level 2 | States, municipalities, and political subdivisions
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	2,677		1,711
Level 3
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	175		201
Equity securities	3		13
Short-term investments
Other investments	2,252		1,877
Securities lending collateral
Investment derivative instruments
Other derivative instruments			3
Separate account assets
Total assets measured at fair value	2,430		2,094
GLB	1,119	[1]	1,319	[1]
Level 3 | U.S. Treasury and agency
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value			5
Level 3 | Foreign
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	60		33
Level 3 | Corporate securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	102		134
Level 3 | Mortgage backed-securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	13		28
Level 3 | States, municipalities, and political subdivisions
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value			1
Total
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	47,306		41,967
Equity securities	744		647
Short-term investments	2,228		2,301
Other investments	2,716		2,314
Securities lending collateral	1,791		1,375
Investment derivative instruments	11		10
Other derivative instruments	24		41
Separate account assets	943		660
Total assets measured at fair value	55,763		49,315
GLB	1,119	[1]	1,319	[1]
Total | U.S. Treasury and agency
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	3,735		2,960
Total | Foreign
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	13,713		12,401
Total | Corporate securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	16,708		14,693
Total | Mortgage backed-securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	10,473		10,201
Total | States, municipalities, and political subdivisions
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	$ 2,677		$ 1,712

[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 c) for additional information.