Note 7 - Available-for-Sale Investments (Details Textual) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2016	Jun. 30, 2015
Asset-backed Securities [Member]
Available-for-Sale Securities, Maturity Term	10 years
Proceeds from Sale of Short-term Investments	$ 121	$ 825

The cash inflow from sales of all investments, including securities and other assets, having ready marketability and intended by management to be liquidated, if necessary, within the current operating cycle. Includes cash flows from securities classified as trading securities that were acquired for reasons other than sale in the short-term.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Investing Activities
-URI http://asc.fasb.org/extlink&oid=6516133

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3179-108585

Name:	us-gaap_ProceedsFromSaleOfShortTermInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration