Share Buyback Program (Details) shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) Program shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares	Nov. 26, 2008 shares
Share Buyback Program (Textual) [Abstract]
Common stock available for repurchase (in shares) | shares	341			1,000
Number of other repurchase programs outstanding | Program	0
Number of stock repurchase programs other expired | Program	0
Stock repurchased during period, shares | shares	0	0	0
Stock repurchased during period, value | $	$ 0	$ 0	$ 0