Accumulated Other Comprehensive Loss - Reclassification out of Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Reclassification Adjustment Out of AOCI [Line Items]
Operating Revenues	$ 324	$ 385	$ 315	$ 307	$ 280	$ 340	$ 324	$ 343	$ 1,331	$ 1,287	$ 1,653
Other Cost and Expense, Operating									(405)	(495)	(571)
Income Tax Expense (Benefit)									93	(160)	441
Net Income (Loss)	(27)	(448)	(84)	(82)	(561)	(162)	(104)	(82)	(641)	(909)	(1,079)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) [Member]
Reclassification Adjustment Out of AOCI [Line Items]
Other Cost and Expense, Operating									(3)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gain (Losses) on Cash Flow Hedges
Reclassification Adjustment Out of AOCI [Line Items]
Income Tax Expense (Benefit)									3
Net Income (Loss)									(5)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gain (Losses) on Cash Flow Hedges | Electricity
Reclassification Adjustment Out of AOCI [Line Items]
Operating Revenues									(3)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gain (Losses) on Cash Flow Hedges | Interest Expense [Member]
Reclassification Adjustment Out of AOCI [Line Items]
Interest Expense									(5)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrecognized Losses and Prior Service Adjustments, Net
Reclassification Adjustment Out of AOCI [Line Items]
Income Tax Expense (Benefit)									3
Net Income (Loss)									(5)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment, Net Actuarial Gains (Losses) [Member]
Reclassification Adjustment Out of AOCI [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Gain (Loss), before Tax									(5)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment, Net Actuarial Gains (Losses) [Member] | Plant Operations [Member]
Reclassification Adjustment Out of AOCI [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Gain (Loss), before Tax									5
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment, Net Actuarial Gains (Losses) [Member] | General and Administrative Expense [Member]
Reclassification Adjustment Out of AOCI [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Gain (Loss), before Tax									3
Midwest Generation LLC [Member]
Reclassification Adjustment Out of AOCI [Line Items]
Operating Revenues	203	232	203	179	193	253	213	233	817	892	1,286
Interest Expense									(23)	(33)	(40)
Other Cost and Expense, Operating									(258)	(369)	(457)
Income Tax Expense (Benefit)	17	1	(1)	0	23	7	27	5	17	62	172
Net Income (Loss)	(14)	(471)	(74)	(74)	(1,401)	(12)	(42)	(9)	(633)	(1,464)	(270)
Midwest Generation LLC [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) [Member]
Reclassification Adjustment Out of AOCI [Line Items]
Other Cost and Expense, Operating									(1)
Income Tax Expense (Benefit)									1
Net Income (Loss)									(3)
Midwest Generation LLC [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gain (Losses) on Cash Flow Hedges
Reclassification Adjustment Out of AOCI [Line Items]
Income Tax Expense (Benefit)									2
Net Income (Loss)									(2)
Midwest Generation LLC [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gain (Losses) on Cash Flow Hedges | Electricity
Reclassification Adjustment Out of AOCI [Line Items]
Operating Revenues									(4)
Midwest Generation LLC [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment, Net Actuarial Gains (Losses) [Member]
Reclassification Adjustment Out of AOCI [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Gain (Loss), before Tax									$ (3)