Fair Value Measurements (Financial Instruments Measured At Fair Value On Recurring Basis) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	$ 49,395		$ 49,254
Equity securities	510		837
Short-term investments	2,322		1,763
Other investments	3,346		2,976
Securities lending collateral	1,330		1,632
Level 1
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	1,680		1,849
Equity securities	492		373
Short-term investments	1,183		953
Other investments	370		305
Investment derivative instruments, assets	18		19
Separate account assets	1,400		1,145
Total assets measured at fair value	5,143		4,644
Investment derivative instruments, liability	36		6
Other derivative instruments, liability	21		60
GLB			0	[1]
Total liabilities measured at fair value	57		66
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	1,680		1,626
Level 1 | Foreign
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value			223
Level 2
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	47,491		47,187
Equity securities	16		460
Short-term investments	1,139		803
Other investments	257		231
Securities lending collateral	1,330		1,632
Other derivative instruments, assets	2		6
Separate account assets	90		81
Total assets measured at fair value	50,325		50,400
Other derivative instruments, liability			2
GLB			0	[1]
Total liabilities measured at fair value			2
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	1,140		1,323
Level 2 | Foreign
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	15,220		14,324
Level 2 | Corporate securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	17,244		17,304
Level 2 | Mortgage backed-securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	10,271		10,886
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	3,616		3,350
Level 3
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	224		218
Equity securities	2		4
Short-term investments			7
Other investments	2,719		2,440
Total assets measured at fair value	2,945		2,669
Other derivative instruments, liability	4
GLB	406	[1]	193	[1]
Total liabilities measured at fair value	410		193
Level 3 | Foreign
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	22		44
Level 3 | Corporate securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	187		166
Level 3 | Mortgage backed-securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	15		8
Total
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	49,395		49,254
Equity securities	510		837
Short-term investments	2,322		1,763
Other investments	3,346		2,976
Securities lending collateral	1,330		1,632
Investment derivative instruments, assets	18		19
Other derivative instruments, assets	2		6
Separate account assets	1,490		1,226
Total assets measured at fair value	58,413		57,713
Investment derivative instruments, liability	36		6
Other derivative instruments, liability	25		62
GLB	406	[1]	193	[1]
Total liabilities measured at fair value	467		261
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	2,820		2,949
Total | Foreign
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	15,242		14,591
Total | Corporate securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	17,431		17,470
Total | Mortgage backed-securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	10,286		10,894
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	$ 3,616		$ 3,350

[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.