v3.2.0.727
Long-term Debt (Details) - USD ($)
$ in Millions
6 Months Ended
Jun. 30, 2015
Dec. 31, 2014
New revolving credit facility    
Long-term debt    
Outstanding balance $ 0 $ 0
Maximum amount of the Credit Facility 1,000  
Letter of credit    
Long-term debt    
Current borrowing capacity $ 150  
Line of credit | Minimum    
Long-term debt    
Commitment fees on the unused portion (as a percent) 0.25%  
Line of credit | Maximum    
Long-term debt    
Commitment fees on the unused portion (as a percent) 0.375%