Quarterly report pursuant to Section 13 or 15(d)

Changes in Level 3 Instruments Measured on a Recurring Basis (Detail)

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Changes in Level 3 Instruments Measured on a Recurring Basis (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Jun. 30, 2012
Jun. 30, 2011
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Beginning Balance $ 204 $ 254 $ 217 $ 405
Transfers into (out of) Level 3 0 0 0 0
Net realized and unrealized gains (losses):        
Included in earnings (in investment income) (14) (14) (27) (27)
Included in accumulated other comprehensive income (pre-tax) 0 0 0 0
Purchases 0 0 0 0
Sales 0 0 0 (138)
Ending Balance 190 240 190 240
Marketable securities
       
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Beginning Balance 0 0 0 138
Transfers into (out of) Level 3 0 0 0 0
Net realized and unrealized gains (losses):        
Included in earnings (in investment income) 0 0 0 0
Included in accumulated other comprehensive income (pre-tax) 0 0 0 0
Purchases 0 0 0 0
Sales 0 0 0 (138)
Ending Balance 0 0 0 0
Other Long-term Investments
       
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Beginning Balance 204 254 217 267
Transfers into (out of) Level 3 0 0 0 0
Net realized and unrealized gains (losses):        
Included in earnings (in investment income) (14) (14) (27) (27)
Included in accumulated other comprehensive income (pre-tax) 0 0 0 0
Purchases 0 0 0 0
Sales 0 0 0 0
Ending Balance $ 190 $ 240 $ 190 $ 240