Long-term Debt - Summary of Long-term Debt (Detail) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Long-term debt, carrying amount	$ 16,600	$ 16,463
Commercial paper borrowings
Debt Instrument [Line Items]
Long-term debt, carrying amount	2,833	2,421
4.00% Senior Notes due 2025
Debt Instrument [Line Items]
Long-term debt, carrying amount	1,741	1,740
3.30% Senior Notes due 2021
Debt Instrument [Line Items]
Long-term debt, carrying amount	1,594	1,594
3.00% Senior Notes due 2020
Debt Instrument [Line Items]
Long-term debt, carrying amount	1,591	1,591
3.65% Senior Notes due 2023
Debt Instrument [Line Items]
Long-term debt, carrying amount	1,491	1,491
2.35% Senior Notes due 2018
Debt Instrument [Line Items]
Long-term debt, carrying amount	1,298	1,297
4.20% Senior Notes due 2021
Debt Instrument [Line Items]
Long-term debt, carrying amount	1,100	1,100
2.40% Senior Notes due 2022
Debt Instrument [Line Items]
Long-term debt, carrying amount	996	996
3.63% Senior Notes due 2022
Debt Instrument [Line Items]
Long-term debt, carrying amount	845	845
0.63% Guaranteed Notes due 2019
Debt Instrument [Line Items]
Long-term debt, carrying amount	680	622
1.50% Guaranteed Notes due 2019
Debt Instrument [Line Items]
Long-term debt, carrying amount	580	536
6.38% Notes due 2018
Debt Instrument [Line Items]
Long-term debt, carrying amount	294	297
7.00% Notes due 2038
Debt Instrument [Line Items]
Long-term debt, carrying amount	213	214
Other
Debt Instrument [Line Items]
Long-term debt, carrying amount	746	1,118
4.50% Notes due 2021
Debt Instrument [Line Items]
Long-term debt, carrying amount	136	137
5.95% Notes due 2041
Debt Instrument [Line Items]
Long-term debt, carrying amount	115	116
3.60% Notes due 2022
Debt Instrument [Line Items]
Long-term debt, carrying amount	110	110
5.13% Notes due 2043
Debt Instrument [Line Items]
Long-term debt, carrying amount	99	99
4.00% Notes due 2023
Debt Instrument [Line Items]
Long-term debt, carrying amount	82	83
3.70% Notes due 2024
Debt Instrument [Line Items]
Long-term debt, carrying amount	$ 56	$ 56