Investments - Average Coupon Rate Percentage and the Average Days to Maturity of Debt (Detail) |
12 Months Ended | |
|---|---|---|
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| Commercial Paper [Member] | ||
| Schedule of Available-for-sale Securities [Line Items] | ||
| Average Coupon Rate | 1.001% | 0.553% |
| Average Days To Maturity | 184 days | 154 days |
| US Government Agencies [Member] | ||
| Schedule of Available-for-sale Securities [Line Items] | ||
| Average Coupon Rate | 0.97% | 0.865% |
| Average Days To Maturity | 400 days | 599 days |
| Corporate Bonds and Notes [Member] | ||
| Schedule of Available-for-sale Securities [Line Items] | ||
| Average Coupon Rate | 1.745% | 1.757% |
| Average Days To Maturity | 318 days | 331 days |