Fair Value Measurements (Financial Instruments Measured At Fair Value On Recurring Basis) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	$ 48,529		$ 47,306
Equity securities, at fair value	831		744
Short-term investments	1,774		2,228
Other investments	2,902		2,716
Securities lending collateral	1,517		1,791
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	1,851		2,292
Equity securities, at fair value	375		253
Short-term investments	1,061		1,503
Other investments	292		268
Investment derivative instruments	(18)		11
Other derivative instruments	7		(6)
Separate account assets	1,074		872
Total assets measured at fair value	4,642		5,193
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	1,615		2,050
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	235		222
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	1		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	46,506		44,839
Equity securities, at fair value	452		488
Short-term investments	705		725
Other investments	221		196
Securities lending collateral	1,517		1,791
Other derivative instruments	8		30
Separate account assets	78		71
Total assets measured at fair value	49,487		48,140
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	1,364		1,685
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	14,324		13,431
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	17,144		16,586
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	10,370		10,460
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	3,304		2,677
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	172		175
Equity securities, at fair value	4		3
Short-term investments	8
Other investments	2,389		2,252
Other derivative instruments	0		0
Total assets measured at fair value	2,573		2,430
GLB	514	[1]	1,119	[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		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	42		60
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	121		102
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	9		13
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	48,529		47,306
Equity securities, at fair value	831		744
Short-term investments	1,774		2,228
Other investments	2,902		2,716
Securities lending collateral	1,517		1,791
Investment derivative instruments	(18)		11
Other derivative instruments	15		24
Separate account assets	1,152		943
Total assets measured at fair value	56,702		55,763
GLB	514	[1]	1,119	[1]
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	2,979		3,735
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	14,601		13,713
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	17,266		16,708
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	10,379		10,473
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	$ 3,304		$ 2,677

[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.