Fair Value Measurements (Financial Instruments Measured At Fair Value On Recurring Basis) (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015		Dec. 31, 2014
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Document Period End Date	Sep. 30, 2015
Available for sale, Fair Value	$ 48,278		$ 49,395
Equity securities, at fair value	464		510
Short-term investments	1,808		2,322
Other investments excluding assets calculated using NAV	741	[1]	785	[2]
Securities lending collateral	1,011		1,330
Investment derivative instruments, assets	17		18
Other derivative instruments, assets	26		2
Separate account assets	1,506		1,490
Total assets measured at fair value	53,851	[1]	55,852	[2]
Investment derivative instruments, liabilities	27		36
Other derivative instruments, liability	7		25
GLB	744	[3]	406	[4]
Total liabilities measured at fair value	778		467
Fair Value, Inputs, Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	1,919		1,680
Equity securities, at fair value	455		492
Short-term investments	703		1,183
Other investments excluding assets calculated using NAV	314	[1]	370	[2]
Securities lending collateral	0		0
Investment derivative instruments, assets	17		18
Other derivative instruments, assets	26		0
Separate account assets	1,423		1,400
Total assets measured at fair value	4,857	[1]	5,143	[2]
Investment derivative instruments, liabilities	27		36
Other derivative instruments, liability	0		21
GLB	0	[3]	0	[4]
Total liabilities measured at fair value	27		57
Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	46,069		47,491
Equity securities, at fair value	5		16
Short-term investments	1,105		1,139
Other investments excluding assets calculated using NAV	218	[1]	211	[2]
Securities lending collateral	1,011		1,330
Investment derivative instruments, assets	0		0
Other derivative instruments, assets	0		2
Separate account assets	83		90
Total assets measured at fair value	48,491	[1]	50,279	[2]
Investment derivative instruments, liabilities	0		0
Other derivative instruments, liability	0		0
GLB	0	[3]	0	[4]
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]
Available for sale, Fair Value	290		224
Equity securities, at fair value	4		2
Short-term investments	0		0
Other investments excluding assets calculated using NAV	209	[1]	204	[2]
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	503	[1]	430	[2]
Investment derivative instruments, liabilities	0		0
Other derivative instruments, liability	7		4
GLB	744	[3]	406	[4]
Total liabilities measured at fair value	751		410
U.S. Treasury And Agency [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	2,885		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]
Available for sale, Fair Value	1,919		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]
Available for sale, Fair Value	966		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]
Available for sale, Fair Value	0		0
Foreign [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	14,291		15,242
Foreign [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	0		0
Foreign [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	14,238		15,220
Foreign [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	53		22
Corporate Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	16,892		17,431
Corporate Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	0		0
Corporate Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	16,709		17,244
Corporate Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	183		187
Collateralized Mortgage Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	11,119		10,286
Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	0		0
Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	11,065		10,271
Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	54		15
States, Municipalities, And Political Subdivisions [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	3,091		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]
Available for sale, 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]
Available for sale, Fair Value	3,091		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]
Available for sale, Fair Value	$ 0		$ 0

[1] Excluded from the table above are partially-owned investments, investment funds, and limited partnerships of $2,504 million and other investments of $25 million at September 30, 2015 measured using NAV. Based on new accounting guidance adopted this quarter, these investments are excluded from the hierarchy table.

[2] (1) Excluded from the table above are partially-owned investments, investment funds, and limited partnerships of $2,561 million at December 31, 2014 measured using NAV. Based on new accounting guidance adopted this quarter, these investments are excluded from the hierarchy table.

[3] 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 liability classified as Future policy benefits in the consolidated balance sheets. Refer to Note 5 for additional information.

[4] 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 liability classified as Future policy benefits in the consolidated balance sheets. Refer to Note 5 for additional information.