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
Sep. 30, 2013
Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]    
Cost $ 1,469 $ 587
Unrealized Gains 2 10
Unrealized Losses (4) 0
Total Estimated Fair Value 1,467 597
U.S. government and agency debt securities
    
Schedule of Available-for-sale Securities [Line Items]    
Cost 342 236
Unrealized Gains 1 2
Unrealized Losses (2) 0
Total Estimated Fair Value 341 238
Mortgage and asset-backed debt securities
    
Schedule of Available-for-sale Securities [Line Items]    
Cost 70 171
Unrealized Gains 0 3
Unrealized Losses (1) 0
Total Estimated Fair Value 69 174
Corporate debt securities
    
Schedule of Available-for-sale Securities [Line Items]    
Cost 713 158
Unrealized Gains 1 5
Unrealized Losses (1) 0
Total Estimated Fair Value 713 163
U.S. state and local municipal debt securities
    
Schedule of Available-for-sale Securities [Line Items]    
Cost 19 15
Unrealized Gains 0 0
Unrealized Losses 0 0
Total Estimated Fair Value 19 15
Other debt and equity securities
    
Schedule of Available-for-sale Securities [Line Items]    
Cost 325 7
Unrealized Gains 0 0
Unrealized Losses 0 0
Total Estimated Fair Value $ 325 $ 7