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
Mar. 31, 2012
Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]    
Cost $ 940 $ 1,232
Unrealized Gains 8 12
Unrealized Losses (1) (3)
Total Estimated Fair Value 947 1,241
U.S. government and agency debt securities
    
Schedule of Available-for-sale Securities [Line Items]    
Cost 216 184
Unrealized Gains 1 3
Unrealized Losses (1) 0
Total Estimated Fair Value 216 187
Mortgage and asset-backed debt securities
    
Schedule of Available-for-sale Securities [Line Items]    
Cost 175 188
Unrealized Gains 3 4
Unrealized Losses 0 (1)
Total Estimated Fair Value 178 191
Corporate debt securities
    
Schedule of Available-for-sale Securities [Line Items]    
Cost 382 835
Unrealized Gains 4 4
Unrealized Losses 0 (2)
Total Estimated Fair Value 386 837
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 152 10
Unrealized Gains 0 1
Unrealized Losses 0 0
Total Estimated Fair Value $ 152 $ 11