Asset Retirement Obligations (ARO Rollforward) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2017 USD ($)
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of period	$ 10,611
Accretion expense	329
Liabilities settled	(430)
Liabilities incurred in the current year	48
Revision in estimates of cash flows	(353)
Balance at end of period	10,205
Duke Energy Carolinas [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of period	3,895
Accretion expense	140
Liabilities settled	(201)
Liabilities incurred in the current year	5
Revision in estimates of cash flows	(238)
Balance at end of period	3,601
Progress Energy [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of period	5,475
Accretion expense	172
Liabilities settled	(193)
Revision in estimates of cash flows	(15)
Balance at end of period	5,439
Duke Energy Progress [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of period	4,697
Accretion expense	147
Liabilities settled	(152)
Revision in estimates of cash flows	(16)
Balance at end of period	4,676
Duke Energy Florida [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of period	778
Accretion expense	25
Liabilities settled	(41)
Revision in estimates of cash flows	1
Balance at end of period	763
Duke Energy Ohio [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of period	77
Accretion expense	3
Liabilities settled	(4)
Liabilities incurred in the current year	7
Revision in estimates of cash flows	(2)
Balance at end of period	81
Duke Energy Indiana [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of period	866
Accretion expense	25
Liabilities settled	(26)
Liabilities incurred in the current year	27
Revision in estimates of cash flows	(99)
Balance at end of period	793
Piedmont Natural Gas [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of period	14
Accretion expense	1
Liabilities settled	(7)
Liabilities incurred in the current year	7
Balance at end of period	$ 15