Debt - Summary of Long-Term Debt (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Sep. 30, 2014
Debt Instrument [Line Items]
Long-Term Debt	$ 11,370	$ 3,768
1.750% Notes due November 8, 2016
Debt Instrument [Line Items]
Long-Term Debt	499	499
1.450% Notes due May 15, 2017
Debt Instrument [Line Items]
Long-Term Debt	300	0
1.800% Notes due December 15, 2017
Debt Instrument [Line Items]
Long-Term Debt	1,246	0
4.900% Notes due April 15, 2018
Debt Instrument [Line Items]
Long-Term Debt	202	202
5.000% Notes due May 15, 2019
Debt Instrument [Line Items]
Long-Term Debt	497	497
6.375% Notes due August 1, 2019
Debt Instrument [Line Items]
Long-Term Debt	802	0
2.675% Notes due December 15, 2019
Debt Instrument [Line Items]
Long-Term Debt	1,244	0
3.250% Notes due November 12, 2020
Debt Instrument [Line Items]
Long-Term Debt	697	697
3.125% Notes due November 8, 2021
Debt Instrument [Line Items]
Long-Term Debt	1,013	997
3.300% Notes due March 1, 2023
Debt Instrument [Line Items]
Long-Term Debt	305	0
3.875% Notes due May 15, 2024
Debt Instrument [Line Items]
Long-Term Debt	419	0
3.734% Notes due December 15, 2024
Debt Instrument [Line Items]
Long-Term Debt	1,739	0
7.000% Debentures due August 1, 2027
Debt Instrument [Line Items]
Long-Term Debt	168	168
6.700% Debentures due August 1, 2028
Debt Instrument [Line Items]
Long-Term Debt	167	167
6.000% Notes due May 15, 2039
Debt Instrument [Line Items]
Long-Term Debt	246	246
5.000% Notes due November 12, 2040
Debt Instrument [Line Items]
Long-Term Debt	296	296
4.875% Notes due May 15, 2044
Debt Instrument [Line Items]
Long-Term Debt	334	0
4.685% Notes due December 15, 2044
Debt Instrument [Line Items]
Long-Term Debt	1,190	0
Other long-term debt
Debt Instrument [Line Items]
Long-Term Debt	$ 5	$ 0