Valuation of Debt and Equity Investments and Certain Liabilities - Additional Information (Details) - USD ($) |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
|
| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | |||
| Credit losses related to available-for-sale investments | $ 0 | $ 0 | $ 0 |
| Proceeds from sales, redemptions and maturities of short-term available-for-sale securities | 3,390,000,000 | 2,892,000,000 | $ 2,966,000,000 |
| Fair Value, Measurements, Recurring | |||
| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | |||
| Total assets fair value | 3,480,000,000 | 3,177,000,000 | |
| Total liabilities fair value | 218,000,000 | 198,000,000 | |
| Fair Value, Measurements, Recurring | Level 3 | |||
| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | |||
| Total assets fair value | 0 | 0 | |
| Total liabilities fair value | $ 0 | $ 0 | |