Employee Benefit Plans (Summary of Accumulated Other Comprehensive Income) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Accumulated other comprehensive (loss) income	$ (234)	$ 2
Duke Energy Corp [Member]
Regulatory assets	4,046	3,390
Regulatory liabilities	3,006	3,155
Qualified Pension Plans [Member]
Deferred income tax asset	10	(143)
Net actuarial loss (gain)	(60)	5
Net amount recognized in accumulated other comprehensive (income)/loss	49	(265)
Qualified Pension Plans [Member] | Regulatory Assets And Deferred Debits And AOCI [Member]
Regulatory assets	1,411	1,259
Deferred income tax asset	(73)	(63)
Prior service credit	4	5
Net actuarial loss (gain)	201	141
Net amount recognized in accumulated other comprehensive (income)/loss	132	83
Accumulated other comprehensive (loss) income	19	17
Non-Qualified Pension Plans [Member]
Regulatory liabilities	7	3
Deferred income tax asset	1	(8)
Net actuarial loss (gain)	(1)	8
Net amount recognized in accumulated other comprehensive (income)/loss		(12)
Non-Qualified Pension Plans [Member] | Regulatory Assets And Deferred Debits And AOCI [Member]
Regulatory assets	25	23
Regulatory liabilities	10	3
Deferred income tax liability		1
Prior service credit		1
Net actuarial loss (gain)	1	(1)
Net amount recognized in accumulated other comprehensive (income)/loss	1	1
Other Post-Retirement Benefit Plans [Member] | Regulatory Assets And Deferred Debits And AOCI [Member]
Regulatory assets	37	59
Regulatory liabilities	107	86
Deferred income tax liability	4	3
Prior service credit	(3)	(3)
Net actuarial loss (gain)	(6)	(7)
Net amount recognized in accumulated other comprehensive (income)/loss	$ (5)	$ (7)