Effect of Adopting ASU 2010-26 in Condensed Consolidated Balance Sheets (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2011	Dec. 31, 2010
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs	$ 483	$ 477	$ 472	$ 458
Total assets	16,022	15,635
Deferred income tax	388	303
Shareholders' equity	5,207	5,033	5,097	5,032
Accounting Standards Update 2010-26
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs	483
Total assets	16,022
Deferred income tax	388
Shareholders' equity	5,207
Accounting Standards Update 2010-26 | As Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs		510
Total assets		15,668
Deferred income tax		314
Shareholders' equity		5,055
Accounting Standards Update 2010-26 | As Adjusted
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs		477
Total assets		15,635
Deferred income tax		303
Shareholders' equity		5,033
Accounting Standards Update 2010-26 | Difference
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs		(33)
Total assets		(33)
Deferred income tax		(11)
Shareholders' equity		$ (22)