Quarterly report pursuant to Section 13 or 15(d)

Summary of Marketable Securities (Detail)

v2.4.0.8
Summary of Marketable Securities (Detail) (USD $)
In Millions, unless otherwise specified
Jun. 30, 2013
Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]    
Cost $ 1,387 $ 587
Unrealized Gains 2 10
Unrealized Losses (5) 0
Total Estimated Fair Value 1,384 597
U.S. government and agency debt securities
    
Schedule of Available-for-sale Securities [Line Items]    
Cost 352 236
Unrealized Gains 1 2
Unrealized Losses (2) 0
Total Estimated Fair Value 351 238
Mortgage and asset-backed debt securities
    
Schedule of Available-for-sale Securities [Line Items]    
Cost 75 171
Unrealized Gains 0 3
Unrealized Losses (1) 0
Total Estimated Fair Value 74 174
Corporate debt securities
    
Schedule of Available-for-sale Securities [Line Items]    
Cost 874 158
Unrealized Gains 1 5
Unrealized Losses (2) 0
Total Estimated Fair Value 873 163
U.S. state and local municipal debt securities
    
Schedule of Available-for-sale Securities [Line Items]    
Cost 17 15
Unrealized Gains 0 0
Unrealized Losses 0 0
Total Estimated Fair Value 17 15
Other debt and equity securities
    
Schedule of Available-for-sale Securities [Line Items]    
Cost 69 7
Unrealized Gains 0 0
Unrealized Losses 0 0
Total Estimated Fair Value $ 69 $ 7