Note 6 - Capital Stock (Details Textual) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions				3 Months Ended		9 Months Ended
	Oct. 19, 2017	Jul. 20, 2017	Apr. 20, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 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				0
Common Stock, Dividends, Per Share, Declared		$ 0.23		$ 0.23	$ 0.22	$ 0.69	$ 0.66
Dividends Payable, Date to be Paid		Aug. 18, 2017
Dividends Payable, Date of Record		Aug. 07, 2017
Subsequent Event [Member]
Common Stock, Dividends, Per Share, Declared	$ 0.23
Dividends Payable, Date to be Paid	Nov. 17, 2017
Dividends Payable, Date of Record	Nov. 03, 2017