Employee Benefit Plans (Fair Value Measurements of Plan Assets - Master Retirement Trust) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 28	$ 38	$ 31
Master Trust [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	9,114	8,655
Alternative Investment, Fair Value Disclosure	1,345	1,300
Master Trust [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	2,189	1,929
Master Trust [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	5,552	5,388
Master Trust [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	28	38
Master Trust [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	2,823	2,472
Alternative Investment, Fair Value Disclosure	847	759
Master Trust [Member] | Equity Securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	1,976	1,677
Master Trust [Member] | Equity Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets		27
Master Trust [Member] | Equity Securities [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets		9
Master Trust [Member] | Corporate Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	4,694	4,330
Master Trust [Member] | Corporate Debt Securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets		8
Master Trust [Member] | Corporate Debt Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	4,694	4,322
Master Trust [Member] | Short Term Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	246	476
Master Trust [Member] | Short Term Investments [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	192	211
Master Trust [Member] | Short Term Investments [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	54	265
Master Trust [Member] | Partnership Interest [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	137	157
Alternative Investment, Fair Value Disclosure	137	157
Master Trust [Member] | Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	226	232
Alternative Investment, Fair Value Disclosure	226	232
Master Trust [Member] | Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	135	144
Alternative Investment, Fair Value Disclosure	135	127
Master Trust [Member] | Real Estate [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets		17
Master Trust [Member] | US Treasury and Government [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	762	734
Master Trust [Member] | US Treasury and Government [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	762	734
Master Trust [Member] | Guaranteed Investment Contracts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	28	29
Master Trust [Member] | Guaranteed Investment Contracts [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	28	29
Master Trust [Member] | Government Bonds - Foreign [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	38	32
Master Trust [Member] | Government Bonds - Foreign [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	38	32
Master Trust [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	6	17
Master Trust [Member] | Cash and Cash Equivalents [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	6	15
Master Trust [Member] | Cash and Cash Equivalents [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets		2
Master Trust [Member] | Asset Backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	2
Master Trust [Member] | Asset Backed Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	2
Master Trust [Member] | Miscellaneous Investments And Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	17	32
Alternative Investment, Fair Value Disclosure		25
Master Trust [Member] | Miscellaneous Investments And Other [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	15	1
Master Trust [Member] | Miscellaneous Investments And Other [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	2	6
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	58	66
OPEB [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	58	66
OPEB [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	28	26
OPEB [Member] | Equity Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	28	26
OPEB [Member] | Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	1	1
OPEB [Member] | Real Estate [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	1	1
OPEB [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	8	14
OPEB [Member] | Cash and Cash Equivalents [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	8	14
OPEB [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	21	25
OPEB [Member] | Debt Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 21	$ 25
Duke Energy Carolinas [Member] | Master Trust [Member]
Defined Benefit Plan Disclosure [Line Items]
Allocated assets	27.00%	27.00%
Progress Energy [Member] | Master Trust [Member]
Defined Benefit Plan Disclosure [Line Items]
Allocated assets	30.00%	30.00%
Duke Energy Progress [Member] | Master Trust [Member]
Defined Benefit Plan Disclosure [Line Items]
Allocated assets	15.00%	15.00%
Duke Energy Florida [Member] | Master Trust [Member]
Defined Benefit Plan Disclosure [Line Items]
Allocated assets	15.00%	15.00%
Duke Energy Ohio [Member] | Master Trust [Member]
Defined Benefit Plan Disclosure [Line Items]
Allocated assets	5.00%	5.00%
Duke Energy Indiana [Member] | Master Trust [Member]
Defined Benefit Plan Disclosure [Line Items]
Allocated assets	8.00%	8.00%
Piedmont Natural Gas [Member] | Master Trust [Member]
Defined Benefit Plan Disclosure [Line Items]
Allocated assets	4.00%