Fair Value Measurements and Investments - Additional Information (Detail) - USD ($)	3 Months Ended
	Dec. 31, 2016	Sep. 30, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable equity investments	$ 48,000,000	$ 46,000,000
Carrying amount, current	2,313,000,000	0
Carrying amount, noncurrent	14,138,000,000	15,882,000,000
Long-term Debt	14,138,000,000	15,882,000,000
Available-for-sale securities, gross unrealized gains	59,000,000	55,000,000
Available-for-sale securities, gross unrealized losses	$ 7,000,000	0
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities, stated maturities	1 year
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities, stated maturities	2 years
Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt	$ 15,885,000,000	15,882,000,000
Long-term Debt, Fair Value	16,304,000,000	17,158,000,000
Senior Notes | 2017 Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying amount, current	1,747,000,000	0
Carrying amount, noncurrent	0	1,746,000,000
Long-term Debt, Fair Value	1,750,000,000	1,754,000,000
Senior Notes | 2020 Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying amount, noncurrent	2,988,000,000	2,988,000,000
Long-term Debt, Fair Value	3,009,000,000	3,077,000,000
Senior Notes | 2022 Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying amount, noncurrent	2,239,000,000	2,238,000,000
Long-term Debt, Fair Value	2,263,000,000	2,359,000,000
Senior Notes | 2025 Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying amount, noncurrent	3,965,000,000	3,964,000,000
Long-term Debt, Fair Value	4,018,000,000	4,225,000,000
Senior Notes | 2035 Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying amount, noncurrent	1,485,000,000	1,485,000,000
Long-term Debt, Fair Value	1,570,000,000	1,698,000,000
Senior Notes | 2045 Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying amount, noncurrent	3,461,000,000	3,461,000,000
Long-term Debt, Fair Value	$ 3,694,000,000	$ 4,045,000,000