Discloses the fair value amount of decommissioning trust assets and other.

Name:	nrg_DecommissioningTrustAssetsAndOther
Namespace Prefix:	nrg
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	nrg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisLineItems
Namespace Prefix:	nrg
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of cash collateral received from hedge counterparties in support of energy risk management activities for which there is an offsetting liability within current liabilities. These amounts are segregated into separate accounts that are not contractually restricted but, based on the entity's intention, are not available for the payment of the entity's general corporate obligations. Depending on market fluctuations and the settlement of the underlying contracts, the entity will refund this collateral to the counterparties pursuant to the terms and conditions of the underlying trades.

+ Details

Name:	nrg_FundsDepositedByCounterparties
Namespace Prefix:	nrg
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Cash and cash equivalents that are held in a separate, bankruptcy-remote subsidiary and pledged as collateral for obligations under a fully funded letter of credit facility.

+ Details

Name:	nrg_RestrictedCashSupportingFundedLetterOfCredit
Namespace Prefix:	nrg
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

+ Details

Name:	us-gaap_AssetsFairValueDisclosure
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_AvailableForSaleSecuritiesAbstract
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Total of debt securities categorized neither as held-to-maturity nor trading which are intended be sold or mature more than one year from the balance sheet date or operating cycle, if longer.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26626-111562

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 12

-Subparagraph b

-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 FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15E

-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 Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 22

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

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15D

-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 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 13

-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 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15C

-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 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 17

-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 9: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 16

-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 10: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6379932&loc=d3e22054-111558

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesDebtSecuritiesNoncurrent
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Entity may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. Compensating balance arrangements that do not legally restrict the withdrawal or usage of cash amounts may be reported as Cash and Cash Equivalents, while legally restricted deposits held as compensating balances against borrowing arrangements, contracts entered into with others, or company statements of intention with regard to particular deposits are not generally reported as cash and cash equivalents. Includes cash and cash equivalents associated with the entity's continuing operations. Excludes cash and cash equivalents associated with the disposal group (and discontinued operation).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.1)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 1

-Article 5

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 7

-Footnote 1

-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 230

-SubTopic 10

-Section 45

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3044-108585

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 8, 9

-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 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section 45

-Paragraph 1

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6361293&loc=d3e6676-107765

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash

-URI http://asc.fasb.org/extlink&oid=6506951

Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 7, 26

-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 9: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

-URI http://asc.fasb.org/extlink&oid=6507016

+ Details

Name:	us-gaap_CashAndCashEquivalentsAtCarryingValue
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of the obligation to return cash collateral under master netting arrangements that have not been offset against net derivative instrument positions.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 8

-URI http://asc.fasb.org/extlink&oid=6935481&loc=d3e41678-113959

-Subparagraph (b)

+ Details

Name:	us-gaap_DerivativeCollateralObligationToReturnCash
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount of the right to reclaim cash collateral under master netting arrangements that have not been offset against net derivative instrument positions.

+ References

+ Details

Name:	us-gaap_DerivativeCollateralRightToReclaimCash
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value of derivative asset, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4B

-Subparagraph (a),(c)

-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5624163-113959

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 44C

-Subparagraph a

-Clause 1

-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 FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 205G

-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

Name:	us-gaap_DerivativeFairValueOfDerivativeAsset
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value of derivative liability, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

+ References

+ Details

Name:	us-gaap_DerivativeFairValueOfDerivativeLiability
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This element represents the aggregate of the liabilities reported on the balance sheet at period end measured at fair value by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

+ Details

Name:	us-gaap_LiabilitiesFairValueDisclosure
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

For an unclassified balance sheet, this item represents investments in common and preferred stocks and other forms of securities that provide ownership interests in a corporation.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 7

-Section 03

-Paragraph 1

-Subparagraph b

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.1(b))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

Name:	us-gaap_MarketableSecuritiesEquitySecurities
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The carrying amounts of cash and cash equivalent items which are restricted as to withdrawal or usage. Restrictions may include legally restricted deposits held as compensating balances against short-term borrowing arrangements, contracts entered into with others, or entity statements of intention with regard to particular deposits; however, time deposits and short-term certificates of deposit are not generally included in legally restricted deposits. Excludes compensating balance arrangements that are not agreements which legally restrict the use of cash amounts shown on the balance sheet. For a classified balance sheet represents the current portion only (the noncurrent portion has a separate concept); there is a separate and distinct element for unclassified presentations.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 1

-Article 5

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

-Publisher AICPA

-Name Audit and Accounting Guide (AAG)

-Number AAG-BRD

-Chapter 4

-Paragraph 80

-Subparagraph Exhibit 4-8, 3

-IssueDate 2006-05-01

-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 FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.1)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Fair Value of Financial Instruments (Details 2) (USD $) In Millions	Sep. 30, 2011	Dec. 31, 2010	Sep. 30, 2010	Dec. 31, 2009
Fair Value Assets and Liabilities, Measured on Recurring Basis
Cash and cash equivalents	$ 1,127	$ 2,951	$ 3,447	$ 2,304
Funds deposited by counterparties	259	408
Restricted cash	441	8
Cash collateral paid in support of energy risk management activities	316	323
Investment in available-for-sale securities (classified within other non-current assets):
Derivative assets	3,121	2,722
Restricted cash supporting Funded Letter of Credit Facility	0	1,300
Cash collateral received in support of energy risk management activities	259	408
Derivative liabilities	2,497	2,050
Level 1
Fair Value Assets and Liabilities, Measured on Recurring Basis
Cash and cash equivalents	1,127	2,951
Funds deposited by counterparties	259	408
Restricted cash	441	8
Cash collateral paid in support of energy risk management activities	316	323
Investment in available-for-sale securities (classified within other non-current assets):
Debt securities	0	0
Marketable equity securities	1	3
Restricted cash supporting Funded Letter of Credit Facility		1,300
Total assets	3,896	5,894
Cash collateral received in support of energy risk management activities	259	408
Total liabilities	1,823	1,068
Level 1 \| Cash and cash equivalents
Investment in available-for-sale securities (classified within other non-current assets):
Trust fund investments	1	9
Level 1 \| U.S. government and federal agency obligations
Investment in available-for-sale securities (classified within other non-current assets):
Trust fund investments	45	27
Level 1 \| Federal agency mortgage-backed securities
Investment in available-for-sale securities (classified within other non-current assets):
Trust fund investments	0	0
Level 1 \| Commercial mortgage-backed securities
Investment in available-for-sale securities (classified within other non-current assets):
Trust fund investments	0	0
Level 1 \| Corporate debt securities
Investment in available-for-sale securities (classified within other non-current assets):
Trust fund investments	0	0
Level 1 \| Marketable equity securities
Investment in available-for-sale securities (classified within other non-current assets):
Trust fund investments	193	213
Level 1 \| Foreign government fixed income securities
Investment in available-for-sale securities (classified within other non-current assets):
Trust fund investments	0	0
Level 1 \| Commodity contracts
Investment in available-for-sale securities (classified within other non-current assets):
Derivative assets	1,513	652
Derivative liabilities	1,564	660
Level 1 \| Interest rate contracts
Investment in available-for-sale securities (classified within other non-current assets):
Derivative liabilities	0	0
Level 2
Fair Value Assets and Liabilities, Measured on Recurring Basis
Cash and cash equivalents	0	0
Funds deposited by counterparties	0	0
Restricted cash	0	0
Cash collateral paid in support of energy risk management activities	0	0
Investment in available-for-sale securities (classified within other non-current assets):
Debt securities	0	0
Marketable equity securities	0	0
Restricted cash supporting Funded Letter of Credit Facility		0
Total assets	1,698	2,172
Cash collateral received in support of energy risk management activities	0	0
Total liabilities	887	1,339
Level 2 \| Cash and cash equivalents
Investment in available-for-sale securities (classified within other non-current assets):
Trust fund investments	0	0
Level 2 \| U.S. government and federal agency obligations
Investment in available-for-sale securities (classified within other non-current assets):
Trust fund investments	0	0
Level 2 \| Federal agency mortgage-backed securities
Investment in available-for-sale securities (classified within other non-current assets):
Trust fund investments	66	57
Level 2 \| Commercial mortgage-backed securities
Investment in available-for-sale securities (classified within other non-current assets):
Trust fund investments	7	11
Level 2 \| Corporate debt securities
Investment in available-for-sale securities (classified within other non-current assets):
Trust fund investments	52	56
Level 2 \| Marketable equity securities
Investment in available-for-sale securities (classified within other non-current assets):
Trust fund investments	0	0
Level 2 \| Foreign government fixed income securities
Investment in available-for-sale securities (classified within other non-current assets):
Trust fund investments	4	2
Level 2 \| Commodity contracts
Investment in available-for-sale securities (classified within other non-current assets):
Derivative assets	1,569	2,046
Derivative liabilities	805	1,251
Level 2 \| Interest rate contracts
Investment in available-for-sale securities (classified within other non-current assets):
Derivative liabilities	82	88
Level 3
Fair Value Assets and Liabilities, Measured on Recurring Basis
Cash and cash equivalents	0	0
Funds deposited by counterparties	0	0
Restricted cash	0	0
Cash collateral paid in support of energy risk management activities	0	0
Investment in available-for-sale securities (classified within other non-current assets):
Debt securities	8	8
Marketable equity securities	0	0
Restricted cash supporting Funded Letter of Credit Facility		0
Total assets	80	71
Cash collateral received in support of energy risk management activities	0	0
Total liabilities	46	51
Level 3 \| Cash and cash equivalents
Investment in available-for-sale securities (classified within other non-current assets):
Trust fund investments	0	0
Level 3 \| U.S. government and federal agency obligations
Investment in available-for-sale securities (classified within other non-current assets):
Trust fund investments	0	0
Level 3 \| Federal agency mortgage-backed securities
Investment in available-for-sale securities (classified within other non-current assets):
Trust fund investments	0	0
Level 3 \| Commercial mortgage-backed securities
Investment in available-for-sale securities (classified within other non-current assets):
Trust fund investments	0	0
Level 3 \| Corporate debt securities
Investment in available-for-sale securities (classified within other non-current assets):
Trust fund investments	0	0
Level 3 \| Marketable equity securities
Investment in available-for-sale securities (classified within other non-current assets):
Trust fund investments	33	39
Level 3 \| Foreign government fixed income securities
Investment in available-for-sale securities (classified within other non-current assets):
Trust fund investments	0	0
Level 3 \| Commodity contracts
Investment in available-for-sale securities (classified within other non-current assets):
Derivative assets	39	24
Derivative liabilities	46	51
Level 3 \| Interest rate contracts
Investment in available-for-sale securities (classified within other non-current assets):
Derivative liabilities	0	0
Fair Value
Fair Value Assets and Liabilities, Measured on Recurring Basis
Cash and cash equivalents	1,127	2,951
Funds deposited by counterparties	259	408
Restricted cash	441	8
Cash collateral paid in support of energy risk management activities	316	323
Investment in available-for-sale securities (classified within other non-current assets):
Debt securities	8	8
Marketable equity securities	1	3
Restricted cash supporting Funded Letter of Credit Facility		1,300
Total assets	5,674	8,137
Cash collateral received in support of energy risk management activities	259	408
Total liabilities	2,756	2,458
Fair Value \| Cash and cash equivalents
Investment in available-for-sale securities (classified within other non-current assets):
Trust fund investments	1	9
Fair Value \| U.S. government and federal agency obligations
Investment in available-for-sale securities (classified within other non-current assets):
Trust fund investments	45	27
Fair Value \| Federal agency mortgage-backed securities
Investment in available-for-sale securities (classified within other non-current assets):
Trust fund investments	66	57
Fair Value \| Commercial mortgage-backed securities
Investment in available-for-sale securities (classified within other non-current assets):
Trust fund investments	7	11
Fair Value \| Corporate debt securities
Investment in available-for-sale securities (classified within other non-current assets):
Trust fund investments	52	56
Fair Value \| Marketable equity securities
Investment in available-for-sale securities (classified within other non-current assets):
Trust fund investments	226	252
Fair Value \| Foreign government fixed income securities
Investment in available-for-sale securities (classified within other non-current assets):
Trust fund investments	4	2
Fair Value \| Commodity contracts
Investment in available-for-sale securities (classified within other non-current assets):
Derivative assets	3,121	2,722
Derivative liabilities	2,415	1,962
Fair Value \| Interest rate contracts
Investment in available-for-sale securities (classified within other non-current assets):
Derivative liabilities	$ 82	$ 88