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		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Underwriting, acquisition and insurance expenses	$ 287	$ 253	$ 561	$ 515
Net income	32	(50)	118	11
Net income per share:
Basic	$ 0.20	$ (0.31)	$ 0.73	$ 0.07
Diluted	$ 0.20	$ (0.31)	$ 0.72	$ 0.07
Accounting Standards Update 2010-26
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Underwriting, acquisition and insurance expenses	287		561
Net income	32		118
Net income per share:
Basic	$ 0.20		$ 0.73
Diluted	$ 0.20		$ 0.72
Scenario, Previously Reported | Accounting Standards Update 2010-26
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Underwriting, acquisition and insurance expenses		251		512
Net income		(49)		13
Net income per share:
Basic		$ (0.30)		$ 0.08
Diluted		$ (0.30)		$ 0.08
Scenario, As Adjusted | Accounting Standards Update 2010-26
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Underwriting, acquisition and insurance expenses		253		515
Net income		(50)		11
Net income per share:
Basic		$ (0.31)		$ 0.07
Diluted		$ (0.31)		$ 0.07
Scenario, Difference | Accounting Standards Update 2010-26
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Underwriting, acquisition and insurance expenses		2		3
Net income		$ (1)		$ (2)
Net income per share:
Basic		$ (0.01)		$ (0.01)
Diluted		$ (0.01)		$ (0.01)