Long-term Debt - Summary of Long-term Debt (Detail) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Long-term debt, carrying amount	$ 17,233	$ 14,442
Commercial paper borrowings
Debt Instrument [Line Items]
Long-term debt, carrying amount	2,624	1,000
4.00% Senior Notes due 2025
Debt Instrument [Line Items]
Long-term debt, carrying amount	1,739	1,741
3.30% Senior Notes due 2021
Debt Instrument [Line Items]
Long-term debt, carrying amount	1,593	1,597
3.00% Senior Notes due 2020
Debt Instrument [Line Items]
Long-term debt, carrying amount	1,590	1,591
3.65% Senior Notes due 2023
Debt Instrument [Line Items]
Long-term debt, carrying amount	1,490	1,496
2.35% Senior Notes due 2018
Debt Instrument [Line Items]
Long-term debt, carrying amount	1,296	1,297
4.20% Senior Notes due 2021
Debt Instrument [Line Items]
Long-term debt, carrying amount	1,099	1,100
1.25% Senior Notes due 2017
Debt Instrument [Line Items]
Long-term debt, carrying amount	999	1,000
2.40% Senior Notes due 2022
Debt Instrument [Line Items]
Long-term debt, carrying amount	995	999
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	669
1.50% Guaranteed Notes due 2019
Debt Instrument [Line Items]
Long-term debt, carrying amount	581	566
1.90% Senior Notes due 2017
Debt Instrument [Line Items]
Long-term debt, carrying amount	498	499
Other
Debt Instrument [Line Items]
Long-term debt, carrying amount	$ 1,215	$ 711