Fair Value Measurements (Financial Instruments Measured At Fair Value On Recurring Basis) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Dec. 31, 2012
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Document Period End Date	Mar. 31, 2013
Fixed maturities available for sale at fair value	$ 47,947		$ 47,306
Equity securities, at fair value	832		744
Short-term investments	2,893		2,228
Other investments	2,820		2,716
Securities lending collateral	1,786		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	2,228		2,292
Equity securities, at fair value	337		253
Short-term investments	2,130		1,503
Other investments	277		268
Investment derivative instruments	(51)		11
Other derivative instruments	(37)		(6)
Separate account assets	947		872
Total assets measured at fair value	5,831		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	1,986		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	223		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	45,553		44,839
Equity securities, at fair value	493		488
Short-term investments	763		725
Other investments	215		196
Securities lending collateral	1,786		1,791
Other derivative instruments	17		30
Separate account assets	69		71
Total assets measured at fair value	48,896		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	1,857		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	13,406		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	16,784		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	10,158		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	3,348		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	166		175
Equity securities, at fair value	2		3
Other investments	2,328		2,252
Other derivative instruments	0		0
Total assets measured at fair value	2,496		2,430
GLB	753	[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	35		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	118		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	13		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	47,947		47,306
Equity securities, at fair value	832		744
Short-term investments	2,893		2,228
Other investments	2,820		2,716
Securities lending collateral	1,786		1,791
Investment derivative instruments	(51)		11
Other derivative instruments	(20)		24
Separate account assets	1,016		943
Total assets measured at fair value	57,223		55,763
GLB	753	[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	3,843		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	13,664		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	16,921		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	10,171		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	$ 3,348		$ 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.