Schedule Of Gross Unrealized Losses And Fair Values Of Securities (Detail) (USD $)
In Millions, unless otherwise specified
Jun. 30, 2012
Dec. 31, 2011
Investment [Line Items]    
Less than 12 months, Fair Value $ 663 $ 625
Less than 12 months, Gross Unrealized Losses (10) (11)
12 months or more, Fair Value 84 135
12 months or more, Gross Unrealized Losses (3) (6)
Total, Fair Value 747 760
Total, Gross Unrealized Losses (13) (17)
Debt Securities | Tax-exempt municipal securities
    
Investment [Line Items]    
Less than 12 months, Fair Value 100 53
Less than 12 months, Gross Unrealized Losses (1) 0
12 months or more, Fair Value 26 48
12 months or more, Gross Unrealized Losses (1) (2)
Total, Fair Value 126 101
Total, Gross Unrealized Losses (2) (2)
Debt Securities | Residential Mortgage-Backed Securities
    
Investment [Line Items]    
Less than 12 months, Fair Value 0 3
Less than 12 months, Gross Unrealized Losses 0 0
12 months or more, Fair Value 22 24
12 months or more, Gross Unrealized Losses (1) (2)
Total, Fair Value 22 27
Total, Gross Unrealized Losses (1) (2)
Debt Securities | Commercial Mortgage-Backed Securities
    
Investment [Line Items]    
Less than 12 months, Fair Value 9 14
Less than 12 months, Gross Unrealized Losses 0 0
12 months or more, Fair Value 0 0
12 months or more, Gross Unrealized Losses 0 0
Total, Fair Value 9 14
Total, Gross Unrealized Losses 0 0
Debt Securities | Asset-backed securities
    
Investment [Line Items]    
Less than 12 months, Fair Value 10 16
Less than 12 months, Gross Unrealized Losses 0 0
12 months or more, Fair Value 0 4
12 months or more, Gross Unrealized Losses 0 0
Total, Fair Value 10 20
Total, Gross Unrealized Losses 0 0
Debt Securities | Corporate Debt Securities
    
Investment [Line Items]    
Less than 12 months, Fair Value 206 355
Less than 12 months, Gross Unrealized Losses (9) (10)
12 months or more, Fair Value 14 41
12 months or more, Gross Unrealized Losses 0 (1)
Total, Fair Value 220 396
Total, Gross Unrealized Losses (9) (11)
Debt Securities | U.S. Treasury And Other U.S. Government Corporations And Agencies | US Treasury And Agency Obligations
    
Investment [Line Items]    
Less than 12 months, Fair Value 94 117
Less than 12 months, Gross Unrealized Losses 0 0
12 months or more, Fair Value 0 0
12 months or more, Gross Unrealized Losses 0 0
Total, Fair Value 94 117
Total, Gross Unrealized Losses 0 0
Debt Securities | U.S. Treasury And Other U.S. Government Corporations And Agencies | Mortgage-Backed Securities
    
Investment [Line Items]    
Less than 12 months, Fair Value 244 67
Less than 12 months, Gross Unrealized Losses 0 (1)
12 months or more, Fair Value 22 18
12 months or more, Gross Unrealized Losses (1) (1)
Total, Fair Value 266 85
Total, Gross Unrealized Losses $ (1) $ (2)