v3.3.0.814
Amortized Cost, Unrealized Gains and Losses, and Fair Value of Available-for-sale Securities (Detail) - USD ($)
$ in Millions
Sep. 30, 2015
Sep. 30, 2014
Schedule of Available-for-sale Securities [Line Items]    
Available-For-Sale Amortized Cost $ 5,808 $ 4,877
Available-for-sale, Gross Unrealized Gains 7 48
Available-for-sale, Gross Unrealized Losses 0 0
Available-for-sale securities 5,815 4,925
Less: current portion of available-for-sale investment securities (2,431) (1,910)
Long-term available-for-sale investment securities 3,384 3,015
US Government-sponsored agency debt securities | Debt and Equity Securities    
Schedule of Available-for-sale Securities [Line Items]    
Available-For-Sale Amortized Cost 2,612 2,160
Available-for-sale, Gross Unrealized Gains 3 2
Available-for-sale securities 2,615 2,162
US Treasury securities | Debt and Equity Securities    
Schedule of Available-for-sale Securities [Line Items]    
Available-For-Sale Amortized Cost 2,652 2,174
Available-for-sale, Gross Unrealized Gains 4 2
Available-for-sale securities 2,656 2,176
Equity securities | Debt and Equity Securities    
Schedule of Available-for-sale Securities [Line Items]    
Available-For-Sale Amortized Cost 4 15
Available-for-sale, Gross Unrealized Gains   43
Available-for-sale securities 4 58
Corporate debt securities | Debt and Equity Securities    
Schedule of Available-for-sale Securities [Line Items]    
Available-For-Sale Amortized Cost 533 521
Available-for-sale, Gross Unrealized Gains   1
Available-for-sale securities 533 522
Auction rate securities | Debt and Equity Securities    
Schedule of Available-for-sale Securities [Line Items]    
Available-For-Sale Amortized Cost 7 7
Available-for-sale securities $ 7 $ 7