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, 2013
Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]    
Cost $ 869 $ 587
Unrealized Gains 8 10
Unrealized Losses (1) 0
Total Estimated Fair Value 876 597
U.S. government and agency debt securities
    
Schedule of Available-for-sale Securities [Line Items]    
Cost 240 236
Unrealized Gains 1 2
Unrealized Losses 0 0
Total Estimated Fair Value 241 238
Mortgage and asset-backed debt securities
    
Schedule of Available-for-sale Securities [Line Items]    
Cost 141 171
Unrealized Gains 2 3
Unrealized Losses 0 0
Total Estimated Fair Value 143 174
Corporate debt securities
    
Schedule of Available-for-sale Securities [Line Items]    
Cost 417 158
Unrealized Gains 4 5
Unrealized Losses 0 0
Total Estimated Fair Value 421 163
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 56 7
Unrealized Gains 1 0
Unrealized Losses (1) 0
Total Estimated Fair Value $ 56 $ 7