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
Mar. 31, 2014
Mar. 31, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning Balance $ 110 $ 163
Transfers into (out of) Level 3 0 0
Net realized and unrealized gains (losses):    
Included in earnings (in investment income) (11) (13)
Included in accumulated other comprehensive income (pre-tax) 0 0
Purchases 0 0
Sales 0 0
Ending Balance 99 150
Marketable securities
    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning Balance 0 0
Transfers into (out of) Level 3 0 0
Net realized and unrealized gains (losses):    
Included in earnings (in investment income) 0 0
Included in accumulated other comprehensive income (pre-tax) 0 0
Purchases 0 0
Sales 0 0
Ending Balance 0 0
Other Long-term Investments
    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning Balance 110 163
Transfers into (out of) Level 3 0 0
Net realized and unrealized gains (losses):    
Included in earnings (in investment income) (11) (13)
Included in accumulated other comprehensive income (pre-tax) 0 0
Purchases 0 0
Sales 0 0
Ending Balance $ 99 $ 150