Commitments and Contingencies (Future Minimum Operating Lease Payments) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]      
Operating leases, rent expense, minimum rentals $ 131 $ 135 $ 175
Real Estate Leases      
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]      
2015 100    
2016 86    
2017 67    
2018 48    
2019 29    
Thereafter 46    
Total 376    
Non-Rental Equipment Leases      
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]      
2015 31    
2016 29    
2017 27    
2018 20    
2019 15    
Thereafter 8    
Total $ 130