Stock Repurchase Plan (Details) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended	0 Months Ended	1 Months Ended	6 Months Ended	1 Months Ended	6 Months Ended
	Jul. 31, 2013 2013 Repurchase Plan	Jun. 30, 2014 2014 Repurchase Plan	Jun. 30, 2014 2014 Repurchase Plan	Jun. 30, 2014 2014 Repurchase Plan	Dec. 31, 2012 2012 Repurchase Plan	Jun. 30, 2013 2012 Repurchase Plan
Stock Repurchase Plan
Additional authorized amount of outstanding common stock to be repurchased			$ 150
Authorized amount to repurchase outstanding common stock	150.0			114.5	50.0
Aggregate shares repurchased				2,764,576		1,573,588
Remaining amount of authorized under 2014 Repurchase Plan		145
Total cost of shares repurchased						$ 50