Accounting Policies - Additional Information (Detail) (USD $) In Millions	Sep. 30, 2011	Jun. 30, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Dec. 31, 2009
Significant Accounting Policies [Line Items]
Deferred policy acquisition costs	$ 512	$ 511	$ 488	$ 469	$ 485	$ 481
Accounting Standards Update 2010-26
Significant Accounting Policies [Line Items]
Deferred policy acquisition costs	100
Accounting Standards Update 2010-26 | Minimum
Significant Accounting Policies [Line Items]
Deferred policy acquisition costs	35
Accounting Standards Update 2010-26 | Maximum
Significant Accounting Policies [Line Items]
Deferred policy acquisition costs	$ 65