Debt - Summary of Long-Term Debt (Detail) - USD ($) $ in Millions	Sep. 30, 2021	Sep. 30, 2020
Debt Instrument [Line Items]
Long-Term Debt	$ 17,110	$ 17,224
3.125% Notes due November 8, 2021
Debt Instrument [Line Items]
Long-Term Debt	0	1,008
2.894% Notes due June 6, 2022
Debt Instrument [Line Items]
Long-Term Debt	0	1,797
Floating Rate Notes due June 6, 2022
Debt Instrument [Line Items]
Long-Term Debt	$ 0	499
1.000% Notes due December 15, 2022
Debt Instrument [Line Items]
Interest rate	1.00%
Long-Term Debt	$ 579	584
3.300% Notes due March 1, 2023
Debt Instrument [Line Items]
Interest rate	3.30%
Long-Term Debt	$ 0	295
1.401% Notes due May 24, 2023
Debt Instrument [Line Items]
Interest rate	1.401%
Long-Term Debt	$ 347	350
0.632% Notes due June 4, 2023
Debt Instrument [Line Items]
Interest rate	0.632%
Long-Term Debt	$ 926	933
Notes 0.000% due August 13, 2023 [Member]
Debt Instrument [Line Items]
Interest rate	0.00%
Long-Term Debt	$ 463	0
3.875% Notes due May 15, 2024
Debt Instrument [Line Items]
Interest rate	3.875%
Long-Term Debt	$ 146	180
3.363% Notes due June 6, 2024
Debt Instrument [Line Items]
Interest rate	3.363%
Long-Term Debt	$ 994	1,742
3.734% Notes due December 15, 2024
Debt Instrument [Line Items]
Interest rate	3.734%
Long-Term Debt	$ 873	1,370
3.020% Notes due May 24, 2025
Debt Instrument [Line Items]
Interest rate	3.02%
Long-Term Debt	$ 336	320
Notes 0.034% due August 13, 2025 [Member]
Debt Instrument [Line Items]
Interest rate	0.034%
Long-Term Debt	$ 577	0
1.208% Notes due June 4, 2026
Debt Instrument [Line Items]
Interest rate	1.208%
Long-Term Debt	$ 693	699
6.700% Notes due December 1, 2026
Debt Instrument [Line Items]
Interest rate	6.70%
Long-Term Debt	$ 168	172
1.900% Notes due December 15, 2026
Debt Instrument [Line Items]
Interest rate	1.90%
Long-Term Debt	$ 577	582
3.700% Notes due June 6, 2027
Debt Instrument [Line Items]
Interest rate	3.70%
Long-Term Debt	$ 1,716	1,715
7.000% Debentures due August 1, 2027
Debt Instrument [Line Items]
Interest rate	7.00%
Long-Term Debt	$ 174	175
6.700% Debentures due August 1, 2028
Debt Instrument [Line Items]
Interest rate	6.70%
Long-Term Debt	$ 173	174
Notes 0.334% due August 13, 2028
Debt Instrument [Line Items]
Interest rate	0.334%
Long-Term Debt	$ 1,037	0
Notes 2.823% due May 20, 2030
Debt Instrument [Line Items]
Interest rate	2.823%
Long-Term Debt	$ 744	743
Notes 1.957% due February 11, 2031
Debt Instrument [Line Items]
Interest rate	1.957%
Long-Term Debt	$ 992	0
Notes 1.213% due February 12, 2036 [Member]
Debt Instrument [Line Items]
Interest rate	1.213%
Long-Term Debt	$ 690	0
6.000% Notes due May 15, 2039
Debt Instrument [Line Items]
Interest rate	6.00%
Long-Term Debt	$ 246	246
5.000% Notes due November 12, 2040
Debt Instrument [Line Items]
Interest rate	5.00%
Long-Term Debt	$ 124	124
Notes 1.336 due August 13, 2041
Debt Instrument [Line Items]
Interest rate	1.336%
Long-Term Debt	$ 1,034	0
4.875% Notes due May 15, 2044
Debt Instrument [Line Items]
Interest rate	4.875%
Long-Term Debt	$ 246	247
4.685% Notes due December 15, 2044
Debt Instrument [Line Items]
Interest rate	4.685%
Long-Term Debt	$ 1,033	1,044
4.669% Notes due June 6, 2047
Debt Instrument [Line Items]
Interest rate	4.669%
Long-Term Debt	$ 1,481	1,485
Notes 3.794% due May 20, 2050
Debt Instrument [Line Items]
Interest rate	3.794%
Long-Term Debt	$ 742	$ 742