Regulatory Matters - Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Regulatory Assets Liabilities [Line Items]
Total current regulatory assets	$ 275	$ 176
Total long-term regulatory assets	3,025	2,374
Total current regulatory liabilities	(48)	(59)
Total long-term regulatory liabilities	(2,700)	(2,635)
Net regulatory (liabilities) assets	552	(144)
Deferred fuel cost
Regulatory Assets Liabilities [Line Items]
Total current regulatory assets	275	169
Nuclear deferral
Regulatory Assets Liabilities [Line Items]
Total current regulatory assets	0	7
Total long-term regulatory assets	117	178
Total current regulatory liabilities	(15)	0
Regulatory noncurrent asset amortization period	Recorded and recovered or amortized as approved by the appropriate state utility commission over a period not exceeding five years.
Non-ARO cost of removal
Regulatory Assets Liabilities [Line Items]
Total long-term regulatory liabilities	(1,650)	(1,857)
Regulatory noncurrent liability amortization period	Asset retirement and removal liabilities are recorded over the related property lives, which may range up to 65 years, and will be settled and adjusted following completion of the related activities.
Deferred impact of ARO
Regulatory Assets Liabilities [Line Items]
Total long-term regulatory assets	137	122
Total long-term regulatory liabilities	(146)	(143)
Regulatory noncurrent asset amortization period	Asset retirement and removal liabilities are recorded over the related property lives, which may range up to 65 years, and will be settled and adjusted following completion of the related activities.
Regulatory noncurrent liability amortization period	Asset retirement and removal liabilities are recorded over the related property lives, which may range up to 65 years, and will be settled and adjusted following completion of the related activities.
Income taxes recoverable through future rates
Regulatory Assets Liabilities [Line Items]
Total long-term regulatory assets	352	302
Regulatory noncurrent asset amortization period	Income taxes recoverable through future rates are recovered over the related property lives, which may range up to 65 years.
Loss on reacquired debt
Regulatory Assets Liabilities [Line Items]
Total long-term regulatory assets	29	31
Regulatory noncurrent asset amortization period	Recovered over either the remaining life of the original issue or, if refinanced, over the life of the new issue, which may range up to 30 years.
Postretirement benefits
Regulatory Assets Liabilities [Line Items]
Total long-term regulatory assets	1,506	1,105
Regulatory noncurrent asset amortization period	Recovered and amortized over the remaining service period of employees. In accordance with a 2009 FPSC order, PEF's 2009 deferred pension expense of $34 million will be amortized to the extent that annual pension expense is less than the $27 million allowance provided for in base rates (See Note 17).
Net nuclear decommissioning trust unrealized gains
Regulatory Assets Liabilities [Line Items]
Total long-term regulatory liabilities	(412)	(421)
Regulatory noncurrent liability amortization period	Related to unrealized gains and losses on NDT funds that are recorded as a regulatory asset or liability, respectively, until the funds are used to decommission a nuclear plant.
Derivative mark-to-market adjustment
Regulatory Assets Liabilities [Line Items]
Total long-term regulatory assets	708	505
Regulatory noncurrent asset amortization period	Related to derivative unrealized gains and losses that are recorded as a regulatory liability or asset, respectively, until the contracts are settled. After contract settlement and consumption of the related fuel, the realized gains or losses are passed through the fuel cost-recovery clause.
Environmental
Regulatory Assets Liabilities [Line Items]
Total current regulatory liabilities	(7)	(45)
Other current regulatory liabilities
Regulatory Assets Liabilities [Line Items]
Total current regulatory liabilities	(7)	(3)
Storm reserve
Regulatory Assets Liabilities [Line Items]
Total long-term regulatory liabilities	(132)	(136)
Regulatory noncurrent liability amortization period	Utilized as storm restoration expenses are incurred.
Other regulatory assets (liabilities)
Regulatory Assets Liabilities [Line Items]
Total long-term regulatory assets	84	74
Total long-term regulatory liabilities	(72)	(78)
DSM / Energy Efficiency
Regulatory Assets Liabilities [Line Items]
Total long-term regulatory assets	92	57
Regulatory noncurrent asset amortization period	Recorded and recovered or amortized as approved by the appropriate state utility commission over a period not exceeding 10 years.
Comprehensive Settlement Agreement Member
Regulatory Assets Liabilities [Line Items]
Total long-term regulatory liabilities	(288)	0
Regulatory noncurrent liability amortization period	Recorded as a result of the 2012 settlement agreement to be refunded to customers through the fuel clause over four years beginning in 2013 (see Note 8C).
Deferred energy conservsation cost
Regulatory Assets Liabilities [Line Items]
Total current regulatory liabilities	(19)	(11)
PEC
Regulatory Assets Liabilities [Line Items]
Total long-term regulatory assets	1,310	987
Total long-term regulatory liabilities	(1,543)	(1,461)
PEF
Regulatory Assets Liabilities [Line Items]
Total current regulatory assets	244	105
Total long-term regulatory assets	1,602	1,387
Total long-term regulatory liabilities	$ (1,071)	$ (1,084)