Fair Value Measurements (Financial Instruments Measured At Fair Value On Recurring Basis) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	$ 49,148		$ 49,254
Equity securities, at fair value	546		837
Short-term investments	2,753		1,763
Other investments	3,259		2,976
Securities lending collateral	1,440		1,632
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	1,692		1,849
Equity securities, at fair value	520		373
Short-term investments	1,253		953
Other investments	336		305
Investment derivative instruments, assets	23		19
Other derivative instruments, assets	11		0
Separate account assets	1,389		1,145
Total assets measured at fair value	5,224		4,644
Investment derivative instruments, liabilities	5		6
Other derivative instruments, liability	0		60
GLB	0	[1]	0	[1]
Total liabilities measured at fair value	5		66
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	1,490		1,626
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	202		223
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	0		0
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	47,221		47,187
Equity securities, at fair value	24		460
Short-term investments	1,500		803
Other investments	252		231
Securities lending collateral	1,440		1,632
Other derivative instruments, assets	2		6
Separate account assets	90		81
Total assets measured at fair value	50,529		50,400
Investment derivative instruments, liabilities	0		0
Other derivative instruments, liability	2		2
GLB	0	[1]	0	[1]
Total liabilities measured at fair value	2		2
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	1,188		1,323
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	15,017		14,324
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	17,130		17,304
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	10,309		10,886
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	3,577		3,350
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	235		218
Equity securities, at fair value	2		4
Short-term investments	0		7
Other investments	2,671		2,440
Other derivative instruments, assets	0		0
Total assets measured at fair value	2,908		2,669
Investment derivative instruments, liabilities	0		0
Other derivative instruments, liability	0		0
GLB	317	[1]	193	[1]
Total liabilities measured at fair value	317		193
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		0
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	12		44
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	208		166
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	15		8
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	0		0
Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	49,148		49,254
Equity securities, at fair value	546		837
Short-term investments	2,753		1,763
Other investments	3,259		2,976
Securities lending collateral	1,440		1,632
Investment derivative instruments, assets	23		19
Other derivative instruments, assets	13		6
Separate account assets	1,479		1,226
Total assets measured at fair value	58,661		57,713
Investment derivative instruments, liabilities	5		6
Other derivative instruments, liability	2		62
GLB	317	[1]	193	[1]
Total liabilities measured at fair value	324		261
Estimate of Fair Value, Fair Value Disclosure [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	2,678		2,949
Estimate of Fair Value, Fair Value Disclosure [Member] | Foreign [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	15,231		14,591
Estimate of Fair Value, Fair Value Disclosure [Member] | Corporate Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	17,338		17,470
Estimate of Fair Value, Fair Value Disclosure [Member] | Mortgage Backed-Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	10,324		10,894
Estimate of Fair Value, Fair Value Disclosure [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	$ 3,577		$ 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 for additional information.