Fair Value Measurements (Financial Instruments Measured At Fair Value Using Significant Unobservable Inputs) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended																											12 Months Ended
	Dec. 31, 2012 U.S. Treasury and agency Available-for-sale Debt Securities	Dec. 31, 2011 U.S. Treasury and agency Available-for-sale Debt Securities	Dec. 31, 2012 Foreign Available-for-sale Debt Securities	Dec. 31, 2011 Foreign Available-for-sale Debt Securities	Dec. 31, 2010 Foreign Available-for-sale Debt Securities	Dec. 31, 2012 Corporate securities Available-for-sale Debt Securities	Dec. 31, 2011 Corporate securities Available-for-sale Debt Securities	Dec. 31, 2010 Corporate securities Available-for-sale Debt Securities	Dec. 31, 2012 Mortgage backed-securities Available-for-sale Debt Securities	Dec. 31, 2011 Mortgage backed-securities Available-for-sale Debt Securities	Dec. 31, 2010 Mortgage backed-securities Available-for-sale Debt Securities	Dec. 31, 2012 States, municipalities, and political subdivisions Available-for-sale Debt Securities	Dec. 31, 2011 States, municipalities, and political subdivisions Available-for-sale Debt Securities	Dec. 31, 2010 States, municipalities, and political subdivisions Available-for-sale Debt Securities	Dec. 31, 2012 Equity securities	Dec. 31, 2011 Equity securities	Dec. 31, 2010 Equity securities	Dec. 31, 2012 Other investments	Dec. 31, 2011 Other investments	Dec. 31, 2010 Other investments	Dec. 31, 2012 Other derivative instruments	Dec. 31, 2011 Other derivative instruments	Dec. 31, 2010 Other derivative instruments	Dec. 31, 2012 Guaranteed Living Benefits [Member]	Dec. 31, 2011 Guaranteed Living Benefits [Member]	Dec. 31, 2010 Guaranteed Living Benefits [Member]	Dec. 31, 2009 Guaranteed Living Benefits [Member]	Dec. 31, 2012 Guaranteed Minimum Income Benefit		Dec. 31, 2011 Guaranteed Minimum Income Benefit		Dec. 31, 2010 Guaranteed Minimum Income Benefit
Assets [Roll Forward]
Balance- Beginning of Period, Assets	$ 5		$ 33	$ 26	$ 59	$ 134	$ 115	$ 168	$ 28	$ 39	$ 21	$ 1	$ 2	$ 3	$ 13	$ 13	$ 12	$ 1,877	$ 1,432	$ 1,149	$ 3	$ 4	$ 14
Transfers into Level 3, Assets			49	9		37	42		22	4		1			2			53
Transfers out of Level 3, Assets	(4)		(13)	(18)		(46)	(4)		(35)	(48)		(1)			(11)
Transfers into (Out of) Level 3, Assets					(14)			(25)			(1)			0			1			0			0
Change in Net Unrealized Gains (Losses) included in OCI, Assets			(1)	(1)	1	6	(2)	9								(1)		55	93	53													[1]
Net Realized Gains/Losses, Assets					1	(1)	(3)	(3)								4	1	(7)	(3)	(7)	(4)	2	2
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings																												(200)	[2]	812	[3]	64	[1]
Purchases, Assets		5	46	23		24	32		9	59					4	5		520	602		3
Sales, Assets			(53)	(3)		(19)	(27)		(7)	(17)					(5)	(8)		(9)	(55)
Settlements, Assets	(1)		(1)	(3)		(33)	(19)		(4)	(9)		(1)	(1)					(237)	(192)		(2)	(3)
Purchases, Sales, Issuances, and Settlements, Net, Assets					(21)			(34)			19			(1)			(1)			237			(12)
Balance-End of Period, Assets		5	60	33	26	102	134	115	13	28	39		1	2	3	13	13	2,252	1,877	1,432		3	4
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets																		(7)	(3)	(7)		(1)	1
Liabilities [Roll Forward]
Balance- Beginning of Period, Liabilities																												1,319	[2],[3]	507	[1],[3]	443	[1]
Transfers into Level 3, Liabilities																													[2]		[3]	0	[1]
Transfers out of Level 3, Liabilities																													[2]		[3]
Changes in Net Unrealized Gain (Losses) included in OCI, Liabilities																													[2]		[3]
Purchases, Liabilities																													[2]		[3]
Sales, Liabilites																													[2]		[3]
Settlements, Liabilities																													[2]		[3]
Purchases, Sales, Issuances, and Settlements, Net, Liabilities																																0	[1]
Balance- End of Period, Liabilities																												1,119	[2]	1,319	[2],[3]	507	[1],[3]
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Liabilities																												(200)	[2]	812	[3]	64	[1]
Reported liabilities																								$ 1,400	$ 1,500	$ 648	$ 559

[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. The liability for GLB reinsurance was $648 million at December 31, 2010 and $559 million at December 31, 2009, which includes a fair value derivative adjustment of $507 million and $443 million, respectively.

[2] 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 c) for additional information.

[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 derivative liability classified as Future policy benefits in the consolidated balance sheets. The liability for GLB reinsurance was $1.5 billion at December 31, 2011 and $648 million at December 31, 2010, which includes a fair value derivative adjustment of $1.3 billion and $507 million, respectively.