Fair Value Measurements (Financial Instruments Measured At Fair Value On Recurring Basis) (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	$ 50,410		$ 49,395
Equity securities, at fair value	536		510
Short-term investments	2,536		2,322
Other investments	3,430		3,346
Securities lending collateral	1,033		1,330
Investment derivative instruments, assets	21		18
Other derivative instruments, assets	1		2
Separate account assets	1,574		1,490
Total assets measured at fair value	59,541		58,413
Investment derivative instruments, liabilities	25		36
Other derivative instruments, liability	7		25
GLB	451	[1]	406	[1]
Total liabilities measured at fair value	483		467
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	1,747		1,680
Equity securities, at fair value	518		492
Short-term investments	1,469		1,183
Other investments	364		370
Securities lending collateral	0		0
Investment derivative instruments, assets	21		18
Other derivative instruments, assets	0		0
Separate account assets	1,488		1,400
Total assets measured at fair value	5,607		5,143
Investment derivative instruments, liabilities	25		36
Other derivative instruments, liability	3		21
GLB	0	[1]	0	[1]
Total liabilities measured at fair value	28		57
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	48,441		47,491
Equity securities, at fair value	16		16
Short-term investments	1,067		1,139
Other investments	277		257
Securities lending collateral	1,033		1,330
Investment derivative instruments, assets	0		0
Other derivative instruments, assets	1		2
Separate account assets	86		90
Total assets measured at fair value	50,921		50,325
Investment derivative instruments, liabilities	0		0
Other derivative instruments, liability	0		0
GLB	0	[1]	0	[1]
Total liabilities measured at fair value	0		0
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	222		224
Equity securities, at fair value	2		2
Short-term investments	0		0
Other investments	2,789		2,719
Securities lending collateral	0		0
Investment derivative instruments, assets	0		0
Other derivative instruments, assets	0		0
Separate account assets	0		0
Total assets measured at fair value	3,013		2,945
Investment derivative instruments, liabilities	0		0
Other derivative instruments, liability	4		4
GLB	451	[1]	406	[1]
Total liabilities measured at fair value	455		410
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	2,889		2,820
U.S. Treasury And Agency [Member] | 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	1,747		1,680
U.S. Treasury And Agency [Member] | 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	1,142		1,140
U.S. Treasury And Agency [Member] | 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	0		0
Foreign [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	14,947		15,242
Foreign [Member] | 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	0		0
Foreign [Member] | 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	14,925		15,220
Foreign [Member] | 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	22		22
Corporate Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	17,999		17,431
Corporate Securities [Member] | 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	0		0
Corporate Securities [Member] | 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	17,832		17,244
Corporate Securities [Member] | 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	167		187
Mortgage Backed-Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fixed maturities available for sale at fair value	10,808		10,286
Mortgage Backed-Securities [Member] | 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	0		0
Mortgage Backed-Securities [Member] | 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	10,775		10,271
Mortgage Backed-Securities [Member] | 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	33		15
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	3,767		3,616
States, Municipalities, And Political Subdivisions [Member] | 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	0		0
States, Municipalities, And Political Subdivisions [Member] | 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	3,767		3,616
States, Municipalities, And Political Subdivisions [Member] | 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	$ 0		$ 0

[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.