Annual report pursuant to Section 13 and 15(d)

Age of Gross Unrealized Losses and Fair Value by Investment Category (Detail)

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Age of Gross Unrealized Losses and Fair Value by Investment Category (Detail) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2011
Gain (Loss) on Investments [Line Items]  
Less Than 12 Months Fair Value $ 667
Less Than 12 Months Unrealized Losses (2)
12 Months or More Fair Value 19
12 Months or More Unrealized Losses (1)
Total Fair Value 686
Total Unrealized Losses (3)
Debt Securities
  
Gain (Loss) on Investments [Line Items]  
Less Than 12 Months Fair Value 667
Less Than 12 Months Unrealized Losses (2)
12 Months or More Fair Value 19
12 Months or More Unrealized Losses (1)
Total Fair Value 686
Total Unrealized Losses (3)
Debt Securities | U.S. government and agency debt securities
  
Gain (Loss) on Investments [Line Items]  
Less Than 12 Months Fair Value 34
Total Fair Value 34
Debt Securities | Asset-backed Securities
  
Gain (Loss) on Investments [Line Items]  
Less Than 12 Months Fair Value 10
12 Months or More Fair Value 11
12 Months or More Unrealized Losses (1)
Total Fair Value 21
Total Unrealized Losses (1)
Debt Securities | Corporate debt securities
  
Gain (Loss) on Investments [Line Items]  
Less Than 12 Months Fair Value 621
Less Than 12 Months Unrealized Losses (2)
12 Months or More Fair Value 7
Total Fair Value 628
Total Unrealized Losses (2)
Debt Securities | Other debt securities
  
Gain (Loss) on Investments [Line Items]  
Less Than 12 Months Fair Value 2
12 Months or More Fair Value 1
Total Fair Value $ 3