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Guarantees and Indemnifications(Narrative) (Details) - USD ($)
$ in Millions
Dec. 31, 2016
Dec. 31, 2015
Liabilities Recorded for Third Party Guarantees [Abstract]    
Face value of guarantees $ 13 $ 21
Surety Bond [Member]    
Guarantor Obligations [Line Items]    
Maximum potential amount of future payments associated with guarantees 44  
Standby Letters Of Credit [Member]    
Guarantor Obligations [Line Items]    
Maximum potential amount of future payments associated with guarantees 485  
Unused letters of credit 77  
Performance Guarantee [Member]    
Guarantor Obligations [Line Items]    
Maximum potential amount of future payments associated with guarantees 333  
Maximum potential of future amounts associated with guarantees with expiration dates 215  
Performance Guarantee [Member] | Less Than Wholly Owned Entity [Member]    
Guarantor Obligations [Line Items]    
Maximum potential amount of future payments associated with guarantees 11  
Indemnification Agreement [Member]    
Guarantor Obligations [Line Items]    
Maximum potential amount of future payments associated with guarantees 96  
Maximum potential amount of future payments associated with guarantees with no expiration date 7  
Spectra Capital [Member] | Performance Guarantee [Member]    
Guarantor Obligations [Line Items]    
Maximum potential amount of future payments associated with guarantees 205  
Progress Energy [Member]    
Liabilities Recorded for Third Party Guarantees [Abstract]    
Face value of guarantees   7
Progress Energy [Member] | Indemnification Agreement [Member]    
Guarantor Obligations [Line Items]    
Maximum potential amount of future payments associated with guarantees 96  
Maximum potential amount of future payments associated with guarantees with no expiration date $ 7  
Duke Energy Florida [Member]    
Liabilities Recorded for Third Party Guarantees [Abstract]    
Face value of guarantees   $ 7