Note 6 - Capital Stock (Details Textual) - USD ($) $ / shares in Units, $ in Millions				3 Months Ended		9 Months Ended
	Oct. 18, 2018	Jul. 19, 2018	Apr. 20, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Oct. 22, 2015
Stock Repurchase Program, Authorized Amount								$ 500
Stock Repurchase Program, Additional Authorized Amount			$ 500
Stock Repurchase Program, Remaining Authorized Repurchase Amount				$ 421		$ 421
Treasury Stock, Shares, Acquired				422,000		842,000
Treasury Stock, Value, Acquired, Cost Method				$ 50		$ 100
Common Stock, Dividends, Per Share, Declared		$ 0.24		$ 0.24	$ 0.23	$ 0.72	$ 0.69
Dividends Payable, Date to be Paid		Aug. 17, 2018
Dividends Payable, Date of Record		Aug. 03, 2018
Subsequent Event [Member]
Common Stock, Dividends, Per Share, Declared	$ 0.24
Dividends Payable, Date to be Paid	Nov. 16, 2018
Dividends Payable, Date of Record	Nov. 09, 2018