Quarterly report pursuant to Section 13 or 15(d)

Summary of Marketable Securities (Detail)

v2.4.0.6
Summary of Marketable Securities (Detail) (USD $)
In Millions, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]    
Cost $ 573 $ 1,232
Unrealized Gains 13 12
Unrealized Losses 0 (3)
Total Estimated Fair Value 586 1,241
U.S. government and agency debt securities
    
Schedule of Available-for-sale Securities [Line Items]    
Cost 242 184
Unrealized Gains 3 3
Unrealized Losses 0 0
Total Estimated Fair Value 245 187
Mortgage and asset-backed debt securities
    
Schedule of Available-for-sale Securities [Line Items]    
Cost 152 188
Unrealized Gains 4 4
Unrealized Losses 0 (1)
Total Estimated Fair Value 156 191
Corporate debt securities
    
Schedule of Available-for-sale Securities [Line Items]    
Cost 157 835
Unrealized Gains 6 4
Unrealized Losses 0 (2)
Total Estimated Fair Value 163 837
U.S. state and local municipal debt securities
    
Schedule of Available-for-sale Securities [Line Items]    
Cost 15 15
Unrealized Gains 0 0
Unrealized Losses 0 0
Total Estimated Fair Value 15 15
Other debt and equity securities
    
Schedule of Available-for-sale Securities [Line Items]    
Cost 7 10
Unrealized Gains 0 1
Unrealized Losses 0 0
Total Estimated Fair Value $ 7 $ 11