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Asset Retirement Obligations (Rollforward)(Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Asset Retirement Obligation [Line Items]    
Balance as of January 1 $ 8,466 $ 4,958
Acquisitions 226 4
Accretion expense 384 246
Liabilities settled (422) (68)
Liabilities incurred in the current year 1,016 3,500
Revisions in estimates of cash flows 594 (174)
Balance as of December 31 10,264 8,466
Duke Energy Carolinas [Member]    
Asset Retirement Obligation [Line Items]    
Balance as of January 1 3,428 1,594
Accretion expense 165 113
Liabilities settled (200)  
Liabilities incurred in the current year 178 1,717
Revisions in estimates of cash flows 347 4
Balance as of December 31 3,918 3,428
Progress Energy [Member]    
Asset Retirement Obligation [Line Items]    
Balance as of January 1 4,711 2,570
Acquisitions 226  
Accretion expense 203 135
Liabilities settled (195) (68)
Liabilities incurred in the current year 282 1,783
Revisions in estimates of cash flows 142 291
Balance as of December 31 5,369 4,711
Duke Energy Progress [Member]    
Asset Retirement Obligation [Line Items]    
Balance as of January 1 3,905 1,737
Acquisitions 204  
Accretion expense 169 97
Liabilities settled (125)  
Liabilities incurred in the current year 282 1,783
Revisions in estimates of cash flows 132 288
Balance as of December 31 4,567 3,905
Duke Energy Florida [Member]    
Asset Retirement Obligation [Line Items]    
Balance as of January 1 806 833
Acquisitions 23  
Accretion expense 34 38
Liabilities settled (70) (68)
Revisions in estimates of cash flows 9 3
Balance as of December 31 802 806
Duke Energy Ohio [Member]    
Asset Retirement Obligation [Line Items]    
Balance as of January 1 27 28
Accretion expense 4 2
Liabilities settled (4)  
Liabilities incurred in the current year 116  
Revisions in estimates of cash flows (18) (3)
Balance as of December 31 125 27
Duke Energy Indiana [Member]    
Asset Retirement Obligation [Line Items]    
Balance as of January 1 32 30
Accretion expense 15 2
Liabilities settled (23)  
Liabilities incurred in the current year 418  
Revisions in estimates of cash flows 83  
Balance as of December 31 $ 525 $ 32