Stock Repurchase Program (Details) (USD $)
Share data in Millions, unless otherwise specified
0 Months Ended
Feb. 04, 2015
Mar. 31, 2015
Feb. 28, 2015
counterparty
Feb. 04, 2015
Jan. 31, 2015
Dec. 31, 2014
Oct. 31, 2014
Jul. 31, 2014
Jan. 31, 2014
Stock Repurchase Program [Abstract]                  
Stock Repurchase Program, Authorized Amount         $ 337,000,000 $ 300,000,000 $ 100,000,000 $ 100,000,000 $ 100,000,000
Accelerated Share Repurchases Agreements, Number of Counterparties     2            
Accelerated Share Repurchases, Agreement Amount     300,000,000            
Accelerated Share Repurchases, Upfront Payment       300,000,000          
Stock Repurchased and Retired During Period, Shares 5.7                
Stock Repurchase Program, Remaining Amount Authorized to be Repurchased   $ 200,000,000