Quarterly report pursuant to Section 13 or 15(d)

Summary of Marketable Securities (Detail)

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Summary of Marketable Securities (Detail) - USD ($)
$ in Millions
Jun. 30, 2015
Dec. 31, 2014
Schedule of Marketable Securities [Line Items]    
Marketable Securities, Amortized Cost Basis $ 2,782 $ 992
Marketable Securities, Gross Unrealized Gain 13 2
Marketable Securities, Gross Unrealized Loss (3) (2)
Total Estimated Fair Value 2,792 992
Other debt and equity securities    
Schedule of Marketable Securities [Line Items]    
Marketable Securities, Amortized Cost Basis 546 48
Marketable Securities, Gross Unrealized Gain 11 0
Marketable Securities, Gross Unrealized Loss (2) 0
Total Estimated Fair Value 555 48
U.S. government and agency debt securities    
Schedule of Marketable Securities [Line Items]    
Marketable Securities, Amortized Cost Basis 319 321
Marketable Securities, Gross Unrealized Gain 1 1
Marketable Securities, Gross Unrealized Loss 0 (1)
Total Estimated Fair Value 320 321
Mortgage and asset-backed debt securities    
Schedule of Marketable Securities [Line Items]    
Marketable Securities, Amortized Cost Basis 82 89
Marketable Securities, Gross Unrealized Gain 0 1
Marketable Securities, Gross Unrealized Loss 0 (1)
Total Estimated Fair Value 82 89
Corporate debt securities    
Schedule of Marketable Securities [Line Items]    
Marketable Securities, Amortized Cost Basis 1,835 534
Marketable Securities, Gross Unrealized Gain 1 0
Marketable Securities, Gross Unrealized Loss (1) 0
Total Estimated Fair Value $ 1,835 $ 534