Note 6 - Capital Stock (Details Textual) - USD ($) $ / shares in Units, $ in Millions			3 Months Ended		6 Months Ended
	Jul. 20, 2017	Apr. 20, 2017	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Oct. 22, 2015
Stock Repurchase Program, Authorized Amount							$ 500
Stock Repurchase Program, Additional Authorized Amount		$ 500
Stock Repurchase Program, Remaining Authorized Repurchase Amount			$ 521		$ 521
Treasury Stock, Shares, Acquired					1,892,000
Dividends Payable, Date of Record		May 05, 2017
Treasury Stock, Value, Acquired					$ 180
Common Stock, Dividends, Per Share, Declared		$ 0.23	$ 0.23	$ 0.22	$ 0.46	$ 0.44
Dividends Payable, Date to be Paid		May 19, 2017
Subsequent Event [Member]
Dividends Payable, Date of Record	Aug. 07, 2017
Common Stock, Dividends, Per Share, Declared	$ 0.23
Dividends Payable, Date to be Paid	Aug. 18, 2017