Debt - Summary of Long-Term Debt (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Debt Instrument [Line Items]
Long-Term Debt	$ 18,667			$ 10,550
1.800% Notes due December 15, 2017
Debt Instrument [Line Items]
Interest rate	1.80%
Long-Term Debt	$ 0			1,248
4.900% Notes due April 15, 2018
Debt Instrument [Line Items]
Interest rate	4.90%
Long-Term Debt	$ 0			201
5.000% Notes due May 15, 2019
Debt Instrument [Line Items]
Interest rate	5.00%
Long-Term Debt	$ 0			498
2.133% Notes due June 6, 2019
Debt Instrument [Line Items]
Interest rate	2.133%
Long-Term Debt	$ 723			0
0.368% Notes due June 6, 2019
Debt Instrument [Line Items]
Interest rate	0.368%	0.368%
Long-Term Debt	$ 823			0
6.375% Notes due August 1, 2019
Debt Instrument [Line Items]
Interest rate	6.375%
Long-Term Debt	$ 0			776
2.675% Notes due December 15, 2019
Debt Instrument [Line Items]
Interest rate	2.675%
Long-Term Debt	$ 1,121			1,245
2.404% Notes due June 5, 2020
Debt Instrument [Line Items]
Interest rate	2.404%
Long-Term Debt	$ 996			0
3.250% Notes due November 12, 2020
Debt Instrument [Line Items]
Interest rate	3.25%
Long-Term Debt	$ 698			698
3.125% Notes due November 8, 2021
Debt Instrument [Line Items]
Interest rate	3.125%
Long-Term Debt	$ 1,003			1,018
2.894% Notes due June 6, 2022
Debt Instrument [Line Items]
Interest rate	2.894%
Long-Term Debt	$ 1,791			0
Floating Rate Notes due June 6, 2022
Debt Instrument [Line Items]
Long-Term Debt	$ 497			0
1.000% Notes due December 15, 2022
Debt Instrument [Line Items]
Interest rate	1.00%		1.00%
Long-Term Debt	$ 586			0
3.300% Notes due March 1, 2023
Debt Instrument [Line Items]
Interest rate	3.30%
Long-Term Debt	$ 296			304
3.875% Notes due May 15, 2024
Debt Instrument [Line Items]
Interest rate	3.875%
Long-Term Debt	$ 182			417
3.363% Notes due June 6, 2024
Debt Instrument [Line Items]
Interest rate	3.363%
Long-Term Debt	$ 1,736			0
3.734% Notes due December 15, 2024
Debt Instrument [Line Items]
Interest rate	3.734%
Long-Term Debt	$ 1,367			1,740
1.900% Notes due December 15, 2026
Debt Instrument [Line Items]
Interest rate	1.90%		1.90%
Long-Term Debt	$ 585			0
3.700% Notes due June 6, 2027
Debt Instrument [Line Items]
Interest rate	3.70%
Long-Term Debt	$ 2,381			0
7.000% Debentures due August 1, 2027
Debt Instrument [Line Items]
Interest rate	7.00%
Long-Term Debt	$ 166			168
6.700% Debentures due August 1, 2028
Debt Instrument [Line Items]
Interest rate	6.70%
Long-Term Debt	$ 164			167
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	$ 296			297
4.875% Notes due May 15, 2044
Debt Instrument [Line Items]
Interest rate	4.875%
Long-Term Debt	$ 331			333
4.685% Notes due December 15, 2044
Debt Instrument [Line Items]
Interest rate	4.685%
Long-Term Debt	$ 1,189			1,190
4.669% Notes due June 6, 2047
Debt Instrument [Line Items]
Interest rate	4.669%
Long-Term Debt	$ 1,484			0
Other long-term debt
Debt Instrument [Line Items]
Long-Term Debt	$ 3			$ 4