Fair Value Measurements (Significant Unobservable Inputs Used in Valuation of Contracts) (Details) - Level 3 [Member] $ in Millions	9 Months Ended
	Sep. 30, 2017 USD ($) $ / MMBTU $ / MWh
Forward Contracts - Power [Member] | Discounted Cash Flow Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Forward price (in dollars per energy unit) | $ / MWh	0
Forward Contracts - Power [Member] | Discounted Cash Flow Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Forward price (in dollars per energy unit) | $ / MWh	87
Forward contracts - Gas [Member] | Discounted Cash Flow Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Forward price (in dollars per energy unit) | $ / MMBTU	1
Forward contracts - Gas [Member] | Discounted Cash Flow Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Forward price (in dollars per energy unit) | $ / MMBTU	6
Option Contracts, Power [Member] | Option Models [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Implied volatilities (percent)	8.00%
Implied correlations (percent)	1.00%
Option Contracts, Power [Member] | Option Models [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Implied volatilities (percent)	227.00%
Implied correlations (percent)	100.00%
Option Contracts, Primarily Gas [Member] | Option Models [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Implied volatilities (percent)	1.00%
Implied correlations (percent)	1.00%
Option Contracts, Primarily Gas [Member] | Option Models [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Implied volatilities (percent)	104.00%
Implied correlations (percent)	100.00%
Full Requirements and Unit Contingent Contracts [Member] | Discounted Cash Flow Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Forward price (in dollars per energy unit) | $ / MWh	(18.53)
Customer migration rate (percent)	0.00%
Full Requirements and Unit Contingent Contracts [Member] | Discounted Cash Flow Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Forward price (in dollars per energy unit) | $ / MWh	205.63
Customer migration rate (percent)	20.00%
Interest Rate Swap [Member] | NextEra Energy Resources [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Liabilities, Fair Value Disclosure	$ 128
Derivative Financial Instruments, Liabilities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Liabilities, Fair Value Disclosure	502
Derivative Financial Instruments, Liabilities [Member] | Forward Contracts - Power [Member] | Discounted Cash Flow Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Liabilities, Fair Value Disclosure	263
Derivative Financial Instruments, Liabilities [Member] | Forward contracts - Gas [Member] | Discounted Cash Flow Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Liabilities, Fair Value Disclosure	14
Derivative Financial Instruments, Liabilities [Member] | Option Contracts, Power [Member] | Option Models [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Liabilities, Fair Value Disclosure	19
Derivative Financial Instruments, Liabilities [Member] | Option Contracts, Primarily Gas [Member] | Option Models [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Liabilities, Fair Value Disclosure	195
Derivative Financial Instruments, Liabilities [Member] | Full Requirements and Unit Contingent Contracts [Member] | Discounted Cash Flow Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Liabilities, Fair Value Disclosure	11
Derivative Financial Instruments, Assets [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	1,410
Derivative Financial Instruments, Assets [Member] | Forward Contracts - Power [Member] | Discounted Cash Flow Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	860
Derivative Financial Instruments, Assets [Member] | Forward contracts - Gas [Member] | Discounted Cash Flow Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	28
Derivative Financial Instruments, Assets [Member] | Option Contracts, Power [Member] | Option Models [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	48
Derivative Financial Instruments, Assets [Member] | Option Contracts, Primarily Gas [Member] | Option Models [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	149
Derivative Financial Instruments, Assets [Member] | Full Requirements and Unit Contingent Contracts [Member] | Discounted Cash Flow Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	$ 325