Debt - Summary of Long-Term Debt (Detail II)	Sep. 30, 2015
1.750% Notes due November 8, 2016
Debt Instrument [Line Items]
Interest rates of debt instruments	1.75%
1.800% Notes due December 15, 2017
Debt Instrument [Line Items]
Interest rates of debt instruments	1.80%
1.450% Notes due May 15, 2017
Debt Instrument [Line Items]
Interest rates of debt instruments	1.45%
4.900% Notes due April 15, 2018
Debt Instrument [Line Items]
Interest rates of debt instruments	4.90%
5.000% Notes due May 15, 2019
Debt Instrument [Line Items]
Interest rates of debt instruments	5.00%
6.375% Notes due August 1, 2019
Debt Instrument [Line Items]
Interest rates of debt instruments	6.375%
2.675% Notes due December 15, 2019
Debt Instrument [Line Items]
Interest rates of debt instruments	2.675%
3.250% Notes due November 12, 2020
Debt Instrument [Line Items]
Interest rates of debt instruments	3.25%
3.125% Notes due November 8, 2021
Debt Instrument [Line Items]
Interest rates of debt instruments	3.125%
3.300% Notes due March 1, 2023
Debt Instrument [Line Items]
Interest rates of debt instruments	3.30%
3.875% Notes due May 15, 2024
Debt Instrument [Line Items]
Interest rates of debt instruments	3.875%
3.734% Notes due December 15, 2024
Debt Instrument [Line Items]
Interest rates of debt instruments	3.734%
7.000% Debentures due August 1, 2027
Debt Instrument [Line Items]
Interest rates of debt instruments	7.00%
6.700% Debentures due August 1, 2028
Debt Instrument [Line Items]
Interest rates of debt instruments	6.70%
6.000% Notes due May 15, 2039
Debt Instrument [Line Items]
Interest rates of debt instruments	6.00%
5.000% Notes due November 12, 2040
Debt Instrument [Line Items]
Interest rates of debt instruments	5.00%
4.875% Notes due May 15, 2044
Debt Instrument [Line Items]
Interest rates of debt instruments	4.875%
4.685% Notes due December 15, 2044
Debt Instrument [Line Items]
Interest rates of debt instruments	4.685%