Stock Repurchase Plan (Details) - Stock Repurchase Plan [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Nov. 30, 2003
Equity, Class of Treasury Stock [Line Items]
Authorized common stock for repurchases, amount				$ 15
Remaining authorized share for repurchases, amount	$ 70
Number of shares repurchased	0	0	0