Consolidated Statements of Operations and Comprehensive Income (Unaudited) (Parenthetical) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Prior service benefit reclassified to periodic cost, taxes	$ 1.00	$ (4.00)	$ (7.00)
Actuarial loss reclassified to periodic cost, taxes	110.00	93.00	79.00
Transition obligation reclassified to periodic cost, taxes	2.00	2.00	2.00
Pension and non-pension postretirement benefit plan valuation adjustment, taxes	(237.00)	(171.00)	(188.00)
Change in unrealized gain (loss) on cash flow hedges, taxes	(68.00)	39.00	(107.00)
Change in unrealized gain (loss) on marketable securities, taxes	(1.00)	0	0
Change in unrealized gain (loss) on equity investments taxes	1.00	0	0
Exelon Generation Co L L C [Member]
Gain on disposal of discontinued operations, taxes	0	0	0
Change in unrealized gain (loss) on cash flow hedges, taxes	(102.00)	(144.00)	302.00
Commonwealth Edison Co [Member]
Change in unrealized gain (loss) on marketable securities, taxes	0	0	0
PECO Energy Co [Member]
Change in unrealized gain (loss) on marketable securities, taxes	0	0	0
Amortization of realized gain on settled cash flow swaps, taxes	$ 0	$ 0	$ (1.00)

Amount of tax expense or benefit on gain (loss), not previously recognized, resulting from the sale of a business component.

+ References+ Details

Tax effect of the income statement impact of the reclassification adjustment for prior service costs recognized as a component of net period benefit cost.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 130

-Paragraph 25

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 87

-Paragraph 25

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

-Number 51

-Paragraph 38

-Subparagraph c(3)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 12

-URI http://asc.fasb.org/extlink&oid=20435746&loc=d3e640-108580

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 158

-Paragraph 7

-Subparagraph a

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

- Definition

Tax effect of the income statement impact of the reclassification adjustment of accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges realized in net income. Also includes reclassification adjustments of an entity's share of an equity investee's deferred hedging gain (loss) realized in net income.

+ References+ Details

- Definition

Tax effect of the change in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges. Also includes an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

+ References+ Details

- Definition

Tax effect of unrealized holding gain (loss) before reclassification adjustments and transfers on available-for-sale securities.

+ References+ Details