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Risk Management and Fair Values (Assets And Liabilities At Fair Value On A Recurring Basis) (Details) - USD ($)
Sep. 30, 2020
Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash Equivalents, at Carrying Value $ 1,195,805,000 $ 391,480,000
Assets at fair value on a recurring basis    
Restricted Cash and Cash Equivalents, Current 47,000,000 47,000,000
Replacement Reserve Escrow 420,000,000 459,000,000
Equity Securities, FV-NI 959,000,000 905,000,000
Debt Securities 3,127,000,000 2,963,000,000
Liabilities at fair value on a recurring basis    
Assets, Fair Value Disclosure 8,500,000,000 7,430,000,000
Gas Hedge Contracts [Member]    
Liabilities at fair value on a recurring basis    
Liabilities, Fair Value Disclosure on Recurring Basis 1,000,000 7,000,000
Common trust funds valued using Net Asset Value [Domain]    
Assets at fair value on a recurring basis    
Available-for-sale Securities 2,702,000,000 2,536,000,000
Power Contracts Assets [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 28,000,000 118,000,000
Gas Hedge Contracts Assets [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 4,000,000 1,000,000
Fixed Transmission Rights (FTRs) [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 17,000,000 10,000,000
Fair Value Inputs Level 1 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash Equivalents, at Carrying Value 1,196,000,000 391,000,000
Assets at fair value on a recurring basis    
Restricted Cash and Cash Equivalents, Current 47,000,000 47,000,000
Replacement Reserve Escrow 420,000,000 459,000,000
Equity Securities, FV-NI 959,000,000 905,000,000
Debt Securities 1,091,000,000 1,139,000,000
Liabilities at fair value on a recurring basis    
Assets, Fair Value Disclosure 3,716,000,000 2,941,000,000
Fair Value Inputs Level 1 [Member] | Gas Hedge Contracts [Member]    
Liabilities at fair value on a recurring basis    
Liabilities, Fair Value Disclosure on Recurring Basis 0 5,000,000
Fair Value Inputs Level 1 [Member] | Power Contracts Assets [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 0 0
Fair Value Inputs Level 1 [Member] | Gas Hedge Contracts Assets [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 3,000,000 0
Fair Value Inputs Level 1 [Member] | Fixed Transmission Rights (FTRs) [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 0 0
Fair Value, Inputs, Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash Equivalents, at Carrying Value 0 0
Assets at fair value on a recurring basis    
Restricted Cash and Cash Equivalents, Current 0 0
Replacement Reserve Escrow 0 0
Equity Securities, FV-NI 0 0
Debt Securities 2,036,000,000 1,824,000,000
Liabilities at fair value on a recurring basis    
Assets, Fair Value Disclosure 2,037,000,000 1,825,000,000
Fair Value, Inputs, Level 2 [Member] | Gas Hedge Contracts [Member]    
Liabilities at fair value on a recurring basis    
Liabilities, Fair Value Disclosure on Recurring Basis 1,000,000 2,000,000
Fair Value, Inputs, Level 2 [Member] | Power Contracts Assets [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 0 0
Fair Value, Inputs, Level 2 [Member] | Gas Hedge Contracts Assets [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 1,000,000 1,000,000
Fair Value, Inputs, Level 2 [Member] | Fixed Transmission Rights (FTRs) [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 0 0
Fair Value, Inputs, Level 3 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash Equivalents, at Carrying Value 0 0
Assets at fair value on a recurring basis    
Restricted Cash and Cash Equivalents, Current 0 0
Replacement Reserve Escrow 0 0
Equity Securities, FV-NI 0 0
Debt Securities 0 0
Liabilities at fair value on a recurring basis    
Assets, Fair Value Disclosure 45,000,000 128,000,000
Fair Value, Inputs, Level 3 [Member] | Gas Hedge Contracts [Member]    
Liabilities at fair value on a recurring basis    
Liabilities, Fair Value Disclosure on Recurring Basis 0 0
Fair Value, Inputs, Level 3 [Member] | Power Contracts Assets [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 28,000,000 118,000,000
Fair Value, Inputs, Level 3 [Member] | Gas Hedge Contracts Assets [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 0 0
Fair Value, Inputs, Level 3 [Member] | Fixed Transmission Rights (FTRs) [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 17,000,000 10,000,000
Entergy New Orleans [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash Equivalents, at Carrying Value 0 5,991,000
Assets at fair value on a recurring basis    
Restricted Cash and Cash Equivalents, Current 6,165,000 1,989,000
Replacement Reserve Escrow 83,000,000.0 82,600,000
Liabilities at fair value on a recurring basis    
Assets, Fair Value Disclosure 89,300,000 90,900,000
Entergy New Orleans [Member] | Gas Hedge Contracts [Member]    
Liabilities at fair value on a recurring basis    
Liabilities, Fair Value Disclosure on Recurring Basis   200,000
Entergy New Orleans [Member] | Fixed Transmission Rights (FTRs) [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 100,000 300,000
Entergy New Orleans [Member] | Fair Value Inputs Level 1 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash Equivalents, at Carrying Value   6,000,000.0
Assets at fair value on a recurring basis    
Restricted Cash and Cash Equivalents, Current 6,200,000 2,000,000.0
Replacement Reserve Escrow 83,000,000.0 82,600,000
Liabilities at fair value on a recurring basis    
Assets, Fair Value Disclosure 89,200,000 90,600,000
Entergy New Orleans [Member] | Fair Value Inputs Level 1 [Member] | Gas Hedge Contracts [Member]    
Liabilities at fair value on a recurring basis    
Liabilities, Fair Value Disclosure on Recurring Basis   200,000
Entergy New Orleans [Member] | Fair Value Inputs Level 1 [Member] | Fixed Transmission Rights (FTRs) [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 0 0
Entergy New Orleans [Member] | Fair Value, Inputs, Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash Equivalents, at Carrying Value   0
Assets at fair value on a recurring basis    
Restricted Cash and Cash Equivalents, Current 0 0
Replacement Reserve Escrow 0 0
Liabilities at fair value on a recurring basis    
Assets, Fair Value Disclosure 0 0
Entergy New Orleans [Member] | Fair Value, Inputs, Level 2 [Member] | Gas Hedge Contracts [Member]    
Liabilities at fair value on a recurring basis    
Liabilities, Fair Value Disclosure on Recurring Basis   0
Entergy New Orleans [Member] | Fair Value, Inputs, Level 2 [Member] | Fixed Transmission Rights (FTRs) [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 0 0
Entergy New Orleans [Member] | Fair Value, Inputs, Level 3 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash Equivalents, at Carrying Value   0
Assets at fair value on a recurring basis    
Restricted Cash and Cash Equivalents, Current 0 0
Replacement Reserve Escrow 0 0
Liabilities at fair value on a recurring basis    
Assets, Fair Value Disclosure 100,000 300,000
Entergy New Orleans [Member] | Fair Value, Inputs, Level 3 [Member] | Gas Hedge Contracts [Member]    
Liabilities at fair value on a recurring basis    
Liabilities, Fair Value Disclosure on Recurring Basis   0
Entergy New Orleans [Member] | Fair Value, Inputs, Level 3 [Member] | Fixed Transmission Rights (FTRs) [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 100,000 300,000
Entergy Mississippi [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash Equivalents, at Carrying Value 43,022,000 51,590,000
Assets at fair value on a recurring basis    
Replacement Reserve Escrow 80,300,000 80,200,000
Liabilities at fair value on a recurring basis    
Assets, Fair Value Disclosure 125,200,000 132,600,000
Entergy Mississippi [Member] | Gas Hedge Contracts [Member]    
Liabilities at fair value on a recurring basis    
Liabilities, Fair Value Disclosure on Recurring Basis   2,300,000
Entergy Mississippi [Member] | Gas Hedge Contracts Assets [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 1,100,000  
Entergy Mississippi [Member] | Fixed Transmission Rights (FTRs) [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 800,000 800,000
Entergy Mississippi [Member] | Fair Value Inputs Level 1 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash Equivalents, at Carrying Value 43,000,000.0 51,600,000
Assets at fair value on a recurring basis    
Replacement Reserve Escrow 80,300,000 80,200,000
Liabilities at fair value on a recurring basis    
Assets, Fair Value Disclosure 124,400,000 131,800,000
Entergy Mississippi [Member] | Fair Value Inputs Level 1 [Member] | Gas Hedge Contracts [Member]    
Liabilities at fair value on a recurring basis    
Liabilities, Fair Value Disclosure on Recurring Basis   2,300,000
Entergy Mississippi [Member] | Fair Value Inputs Level 1 [Member] | Gas Hedge Contracts Assets [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 1,100,000  
Entergy Mississippi [Member] | Fair Value Inputs Level 1 [Member] | Fixed Transmission Rights (FTRs) [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 0 0
Entergy Mississippi [Member] | Fair Value, Inputs, Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash Equivalents, at Carrying Value 0 0
Assets at fair value on a recurring basis    
Replacement Reserve Escrow 0 0
Liabilities at fair value on a recurring basis    
Assets, Fair Value Disclosure 0 0
Entergy Mississippi [Member] | Fair Value, Inputs, Level 2 [Member] | Gas Hedge Contracts [Member]    
Liabilities at fair value on a recurring basis    
Liabilities, Fair Value Disclosure on Recurring Basis   0
Entergy Mississippi [Member] | Fair Value, Inputs, Level 2 [Member] | Gas Hedge Contracts Assets [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 0  
Entergy Mississippi [Member] | Fair Value, Inputs, Level 2 [Member] | Fixed Transmission Rights (FTRs) [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 0 0
Entergy Mississippi [Member] | Fair Value, Inputs, Level 3 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash Equivalents, at Carrying Value 0 0
Assets at fair value on a recurring basis    
Replacement Reserve Escrow 0 0
Liabilities at fair value on a recurring basis    
Assets, Fair Value Disclosure 800,000 800,000
Entergy Mississippi [Member] | Fair Value, Inputs, Level 3 [Member] | Gas Hedge Contracts [Member]    
Liabilities at fair value on a recurring basis    
Liabilities, Fair Value Disclosure on Recurring Basis   0
Entergy Mississippi [Member] | Fair Value, Inputs, Level 3 [Member] | Gas Hedge Contracts Assets [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 0  
Entergy Mississippi [Member] | Fair Value, Inputs, Level 3 [Member] | Fixed Transmission Rights (FTRs) [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 800,000 800,000
Entergy Louisiana [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash Equivalents, at Carrying Value 251,816,000 1,518,000
Assets at fair value on a recurring basis    
Restricted Cash and Cash Equivalents, Current 9,600,000 3,700,000
Replacement Reserve Escrow 256,700,000 295,900,000
Equity Securities, FV-NI 9,400,000 4,300,000
Debt Securities 626,400,000 601,500,000
Liabilities at fair value on a recurring basis    
Assets, Fair Value Disclosure 2,178,600,000 1,870,200,000
Entergy Louisiana [Member] | Gas Hedge Contracts [Member]    
Liabilities at fair value on a recurring basis    
Liabilities, Fair Value Disclosure on Recurring Basis 1,300,000 4,600,000
Entergy Louisiana [Member] | Common trust funds valued using Net Asset Value [Domain]    
Assets at fair value on a recurring basis    
Available-for-sale Securities 1,014,600,000 958,000,000.0
Entergy Louisiana [Member] | Gas Hedge Contracts Assets [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 3,100,000 800,000
Entergy Louisiana [Member] | Fixed Transmission Rights (FTRs) [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 7,000,000.0 4,500,000
Entergy Louisiana [Member] | Fair Value Inputs Level 1 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash Equivalents, at Carrying Value 251,800,000 1,500,000
Assets at fair value on a recurring basis    
Restricted Cash and Cash Equivalents, Current 9,600,000 3,700,000
Replacement Reserve Escrow 256,700,000 295,900,000
Equity Securities, FV-NI 9,400,000 4,300,000
Debt Securities 162,800,000 180,800,000
Liabilities at fair value on a recurring basis    
Assets, Fair Value Disclosure 692,500,000 486,200,000
Entergy Louisiana [Member] | Fair Value Inputs Level 1 [Member] | Gas Hedge Contracts [Member]    
Liabilities at fair value on a recurring basis    
Liabilities, Fair Value Disclosure on Recurring Basis 0 2,400,000
Entergy Louisiana [Member] | Fair Value Inputs Level 1 [Member] | Gas Hedge Contracts Assets [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 2,200,000 0
Entergy Louisiana [Member] | Fair Value Inputs Level 1 [Member] | Fixed Transmission Rights (FTRs) [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 0 0
Entergy Louisiana [Member] | Fair Value, Inputs, Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash Equivalents, at Carrying Value 0 0
Assets at fair value on a recurring basis    
Restricted Cash and Cash Equivalents, Current 0 0
Replacement Reserve Escrow 0 0
Equity Securities, FV-NI 0 0
Debt Securities 463,600,000 420,700,000
Liabilities at fair value on a recurring basis    
Assets, Fair Value Disclosure 464,500,000 421,500,000
Entergy Louisiana [Member] | Fair Value, Inputs, Level 2 [Member] | Gas Hedge Contracts [Member]    
Liabilities at fair value on a recurring basis    
Liabilities, Fair Value Disclosure on Recurring Basis 1,300,000 2,200,000
Entergy Louisiana [Member] | Fair Value, Inputs, Level 2 [Member] | Gas Hedge Contracts Assets [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 900,000 800,000
Entergy Louisiana [Member] | Fair Value, Inputs, Level 2 [Member] | Fixed Transmission Rights (FTRs) [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 0 0
Entergy Louisiana [Member] | Fair Value, Inputs, Level 3 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash Equivalents, at Carrying Value 0 0
Assets at fair value on a recurring basis    
Restricted Cash and Cash Equivalents, Current 0 0
Replacement Reserve Escrow 0 0
Equity Securities, FV-NI 0 0
Debt Securities 0 0
Liabilities at fair value on a recurring basis    
Assets, Fair Value Disclosure 7,000,000.0 4,500,000
Entergy Louisiana [Member] | Fair Value, Inputs, Level 3 [Member] | Gas Hedge Contracts [Member]    
Liabilities at fair value on a recurring basis    
Liabilities, Fair Value Disclosure on Recurring Basis 0 0
Entergy Louisiana [Member] | Fair Value, Inputs, Level 3 [Member] | Gas Hedge Contracts Assets [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 0 0
Entergy Louisiana [Member] | Fair Value, Inputs, Level 3 [Member] | Fixed Transmission Rights (FTRs) [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 7,000,000.0 4,500,000
Entergy Arkansas [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash Equivalents, at Carrying Value 597,783,000 0
Assets at fair value on a recurring basis    
Restricted Cash and Cash Equivalents, Current 0 4,036,000
Equity Securities, FV-NI 15,100,000 600,000
Debt Securities 433,200,000 412,800,000
Liabilities at fair value on a recurring basis    
Assets, Fair Value Disclosure 1,772,900,000 1,108,600,000
Entergy Arkansas [Member] | Common trust funds valued using Net Asset Value [Domain]    
Assets at fair value on a recurring basis    
Available-for-sale Securities 720,500,000 687,900,000
Entergy Arkansas [Member] | Fixed Transmission Rights (FTRs) [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 6,300,000 3,300,000
Entergy Arkansas [Member] | Fair Value Inputs Level 1 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash Equivalents, at Carrying Value 597,800,000  
Assets at fair value on a recurring basis    
Restricted Cash and Cash Equivalents, Current   4,000,000.0
Equity Securities, FV-NI 15,100,000 600,000
Debt Securities 105,600,000 108,700,000
Liabilities at fair value on a recurring basis    
Assets, Fair Value Disclosure 718,500,000 113,300,000
Entergy Arkansas [Member] | Fair Value Inputs Level 1 [Member] | Fixed Transmission Rights (FTRs) [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 0 0
Entergy Arkansas [Member] | Fair Value, Inputs, Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash Equivalents, at Carrying Value 0  
Assets at fair value on a recurring basis    
Restricted Cash and Cash Equivalents, Current   0
Equity Securities, FV-NI 0 0
Debt Securities 327,600,000 304,100,000
Liabilities at fair value on a recurring basis    
Assets, Fair Value Disclosure 327,600,000 304,100,000
Entergy Arkansas [Member] | Fair Value, Inputs, Level 2 [Member] | Fixed Transmission Rights (FTRs) [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 0 0
Entergy Arkansas [Member] | Fair Value, Inputs, Level 3 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash Equivalents, at Carrying Value 0  
Assets at fair value on a recurring basis    
Restricted Cash and Cash Equivalents, Current   0
Equity Securities, FV-NI 0 0
Debt Securities 0 0
Liabilities at fair value on a recurring basis    
Assets, Fair Value Disclosure 6,300,000 3,300,000
Entergy Arkansas [Member] | Fair Value, Inputs, Level 3 [Member] | Fixed Transmission Rights (FTRs) [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 6,300,000 3,300,000
Entergy Texas [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash Equivalents, at Carrying Value 0 12,904,000
Assets at fair value on a recurring basis    
Restricted Cash and Cash Equivalents, Current 30,864,000 37,720,000
Liabilities at fair value on a recurring basis    
Assets, Fair Value Disclosure 33,200,000 51,500,000
Entergy Texas [Member] | Fixed Transmission Rights (FTRs) [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 2,300,000 900,000
Entergy Texas [Member] | Fair Value Inputs Level 1 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash Equivalents, at Carrying Value   12,900,000
Assets at fair value on a recurring basis    
Restricted Cash and Cash Equivalents, Current 30,900,000 37,700,000
Liabilities at fair value on a recurring basis    
Assets, Fair Value Disclosure 30,900,000 50,600,000
Entergy Texas [Member] | Fair Value Inputs Level 1 [Member] | Fixed Transmission Rights (FTRs) [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 0 0
Entergy Texas [Member] | Fair Value, Inputs, Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash Equivalents, at Carrying Value   0
Assets at fair value on a recurring basis    
Restricted Cash and Cash Equivalents, Current 0 0
Liabilities at fair value on a recurring basis    
Assets, Fair Value Disclosure 0 0
Entergy Texas [Member] | Fair Value, Inputs, Level 2 [Member] | Fixed Transmission Rights (FTRs) [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 0 0
Entergy Texas [Member] | Fair Value, Inputs, Level 3 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash Equivalents, at Carrying Value   0
Assets at fair value on a recurring basis    
Restricted Cash and Cash Equivalents, Current 0 0
Liabilities at fair value on a recurring basis    
Assets, Fair Value Disclosure 2,300,000 900,000
Entergy Texas [Member] | Fair Value, Inputs, Level 3 [Member] | Fixed Transmission Rights (FTRs) [Member]    
Assets at fair value on a recurring basis    
Derivative Asset 2,300,000 900,000
System Energy [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash Equivalents, at Carrying Value 11,813,000 68,441,000
Assets at fair value on a recurring basis    
Equity Securities, FV-NI 8,500,000 13,300,000
Debt Securities 420,800,000 386,200,000
Liabilities at fair value on a recurring basis    
Assets, Fair Value Disclosure 1,126,300,000 1,122,500,000
System Energy [Member] | Common trust funds valued using Net Asset Value [Domain]    
Assets at fair value on a recurring basis    
Available-for-sale Securities 685,200,000 654,600,000
System Energy [Member] | Fair Value Inputs Level 1 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash Equivalents, at Carrying Value 11,800,000 68,400,000
Assets at fair value on a recurring basis    
Equity Securities, FV-NI 8,500,000 13,300,000
Debt Securities 179,100,000 176,300,000
Liabilities at fair value on a recurring basis    
Assets, Fair Value Disclosure 199,400,000 258,000,000.0
System Energy [Member] | Fair Value, Inputs, Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash Equivalents, at Carrying Value 0 0
Assets at fair value on a recurring basis    
Equity Securities, FV-NI 0 0
Debt Securities 241,700,000 209,900,000
Liabilities at fair value on a recurring basis    
Assets, Fair Value Disclosure 241,700,000 209,900,000
System Energy [Member] | Fair Value, Inputs, Level 3 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash Equivalents, at Carrying Value 0 0
Assets at fair value on a recurring basis    
Equity Securities, FV-NI 0 0
Debt Securities 0 0
Liabilities at fair value on a recurring basis    
Assets, Fair Value Disclosure $ 0 $ 0