Fair Value Measurements (Financial Instruments Measured At Fair Value On Recurring Basis) (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	$ 47,016		$ 47,306
Equity securities, at fair value	837		744
Short-term investments	2,425		2,228
Other investments	2,836		2,716
Securities lending collateral	1,662		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	2,047		2,292
Equity securities, at fair value	379		253
Short-term investments	1,442		1,503
Other investments	271		268
Investment derivative instruments	25		11
Other derivative instruments	15		(6)
Separate account assets	961		872
Total assets measured at fair value	5,140		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	1,846		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	182		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	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	44,798		44,839
Equity securities, at fair value	454		488
Short-term investments	974		725
Other investments	216		196
Securities lending collateral	1,662		1,791
Other derivative instruments	24		30
Separate account assets	72		71
Total assets measured at fair value	48,200		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	1,442		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	13,611		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	16,731		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	9,769		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	3,245		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	171		175
Equity securities, at fair value	4		3
Short-term investments	9
Other investments	2,349		2,252
Other derivative instruments	0		0
Total assets measured at fair value	2,533		2,430
GLB	652	[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	48		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	114		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	47,016		47,306
Equity securities, at fair value	837		744
Short-term investments	2,425		2,228
Other investments	2,836		2,716
Securities lending collateral	1,662		1,791
Investment derivative instruments	25		11
Other derivative instruments	39		24
Separate account assets	1,033		943
Total assets measured at fair value	55,873		55,763
GLB	652	[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	3,288		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	13,841		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	16,864		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	9,778		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	$ 3,245		$ 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.