Schedule of Debt Outstanding (Parenthetical) (Detail)	Dec. 31, 2016
5.9% notes due 2016
Debt Instrument [Line Items]
Senior notes, coupon rates	5.90%
0.95% notes due 2016
Debt Instrument [Line Items]
Senior notes, coupon rates	0.95%
1.85% Notes due 2017
Debt Instrument [Line Items]
Senior notes, coupon rates	1.85%
5.375% notes due 2018
Debt Instrument [Line Items]
Senior notes, coupon rates	5.375%
1.85% notes due 2018
Debt Instrument [Line Items]
Senior notes, coupon rates	1.85%
4.5% notes due 2019
Debt Instrument [Line Items]
Senior notes, coupon rates	4.50%
4.25% notes due 2020
Debt Instrument [Line Items]
Senior notes, coupon rates	4.25%
1.7% notes due 2021
Debt Instrument [Line Items]
Senior notes, coupon rates	1.70%
2.40% notes due 2022
Debt Instrument [Line Items]
Senior notes, coupon rates	2.40%
3.2% notes due 2023
Debt Instrument [Line Items]
Senior notes, coupon rates	3.20%
2.6% notes due 2026
Debt Instrument [Line Items]
Senior notes, coupon rates	2.60%
6.625% Debentures due 2028
Debt Instrument [Line Items]
Senior notes, coupon rates	6.625%
7.65% Debentures due 2027
Debt Instrument [Line Items]
Senior notes, coupon rates	7.65%
6.25% notes due 2037
Debt Instrument [Line Items]
Senior notes, coupon rates	6.25%
3.65% Notes due 2042
Debt Instrument [Line Items]
Senior notes, coupon rates	3.65%
4.5% notes due 2043
Debt Instrument [Line Items]
Senior notes, coupon rates	4.50%
3.5% notes due 2046
Debt Instrument [Line Items]
Senior notes, coupon rates	3.50%