XML 88 R72.htm IDEA: XBRL DOCUMENT v3.8.0.1
Valuation of Debt and Equity Investments and Certain Liabilities - Additional Information (Details) - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
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 4,095,000,000 3,390,000,000 $ 2,892,000,000
Fair Value, Measurements, Recurring      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Total assets fair value 4,446,000,000 3,480,000,000  
Total liabilities fair value 255,000,000 218,000,000  
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