Changes In Fair Value Of Assets Measured Using Significant Unobservable Inputs (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 and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Beginning Balance $ 40 $ 65 $ 41 $ 66
Realized in earnings 0 0 0 0
Unrealized in other comprehensive income 0 2 0 2
Purchases 0 17 0 17
Sales 0 (33) (1) (33)
Settlements 0 1 0 0
Ending Balance 40 52 40 52
Private Placements/Venture Capital
        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Beginning Balance 25 14 25 14
Realized in earnings 0 0 0 0
Unrealized in other comprehensive income 0 0 0 0
Purchases 0 17 0 17
Sales 0 0 0 0
Settlements 0 0 0 0
Ending Balance 25 31 25 31
Auction Rate Securities
        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Beginning Balance 15 51 16 52
Realized in earnings 0 0 0 0
Unrealized in other comprehensive income 0 2 0 2
Purchases 0 0 0 0
Sales 0 (33) (1) (33)
Settlements 0 1 0 0
Ending Balance $ 15 $ 21 $ 15 $ 21