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Fair Value Measurements (Fair Value of Instruments Recorded at Carrying Amount) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2018
Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Special use funds: nuclear decommissioning fund assets $ 5,957 $ 6,003
Storm Fund Included In Special Use Funds 78  
Available for sale debt securities amortized cost $ 1,894 1,921
Available For Sale Securities Equity Securities Amortized Cost   1,521
Special Use Funds Nuclear Decommissioning Funds Weighted Average Maturity 8 years  
Estimated Fair Value [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Special Use Funds Fair Value Disclosure $ 833 744
Other Investments Financial Instruments Primarily Notes Receivable Fair Value Disclosure 19 680
Long Term Debt Including Current Maturities Fair Value Disclosure 30,828 35,447
Estimated Fair Value [Member] | Fair Value, Inputs, Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Long Term Debt Including Current Maturities Fair Value Disclosure 30,649 33,743
Carrying Amount [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Special Use Funds Fair Value Disclosure 833 743
Other Investments Financial Instruments Primarily Notes Receivable Fair Value Disclosure 19 500
Long Term Debt Including Current Maturities Fair Value Disclosure 29,226 33,134
FPL [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Special use funds: nuclear decommissioning fund assets 4,061 4,090
Storm Fund Included In Special Use Funds 78  
Available for sale debt securities amortized cost $ 1,469 1,443
Available For Sale Securities Equity Securities Amortized Cost   783
Special Use Funds Nuclear Decommissioning Funds Weighted Average Maturity 8 years  
FPL [Member] | Estimated Fair Value [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Special Use Funds Fair Value Disclosure $ 687 593
Long Term Debt Including Current Maturities Fair Value Disclosure 13,077 13,285
FPL [Member] | Carrying Amount [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Special Use Funds Fair Value Disclosure 687 593
Long Term Debt Including Current Maturities Fair Value Disclosure $ 11,895 $ 11,702