Effect of Adopting ASU 2010-26 in Condensed Consolidated Statements of Comprehensive Operations (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Underwriting, acquisition and insurance expenses	$ 296	$ 260	$ 857	$ 775
NET INCOME	111	19	229	30
Net income per share:
Basic	$ 0.69	$ 0.12	$ 1.41	$ 0.19
Diluted	$ 0.68	$ 0.12	$ 1.40	$ 0.19
Accounting Standards Update 2010-26
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Underwriting, acquisition and insurance expenses	296		857
NET INCOME	111		229
Net income per share:
Basic	$ 0.69		$ 1.41
Diluted	$ 0.68		$ 1.40
Scenario, Previously Reported | Accounting Standards Update 2010-26
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Underwriting, acquisition and insurance expenses		260		772
NET INCOME		19		32
Net income per share:
Basic		$ 0.12		$ 0.20
Diluted		$ 0.12		$ 0.20
Scenario, As Adjusted | Accounting Standards Update 2010-26
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Underwriting, acquisition and insurance expenses		260		775
NET INCOME		19		30
Net income per share:
Basic		$ 0.12		$ 0.19
Diluted		$ 0.12		$ 0.19
Scenario, Difference | Accounting Standards Update 2010-26
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Underwriting, acquisition and insurance expenses		0		3
NET INCOME		$ 0		$ (2)
Net income per share:
Basic		$ 0.00		$ (0.01)
Diluted		$ 0.00		$ (0.01)