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Accounting Policies (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended9 Months Ended12 Months Ended
Sep. 30, 2011
Sep. 30, 2010
Sep. 30, 2011
Securities
CollateralizedLoanObligations
Year
Sep. 30, 2010
Dec. 31, 2010
Dec. 31, 2009
Accounting Policies (Textuals) [Abstract]      
Number of collateralized loan obligation entities  6   
Excess of fair value of assets over liabilities of managed investment entities     $ 261
Weighted average common shares adjustment related to stock-based compensation1.61.31.81.3  
Anti-dilutive potential common shares related to stock-based compensation plans2.63.12.34.0  
Estimated percentage reduction in shareholders' equity from adopting new accounting guidance  3.00% 3.00% 
Maximum [Member]
      
Change in Accounting Estimate [Line Items]      
Estimated percentage reduction in deferred policy acquisition costs from adopting new accounting guidance  20.00% 20.00% 
Minimum [Member]
      
Change in Accounting Estimate [Line Items]      
Estimated percentage reduction in deferred policy acquisition costs from adopting new accounting guidance  15.00% 15.00%