Fair Value Measurements (Significant Unobservable Inputs Used in Valuation of Contracts) (Details) - Level 3 [Member] $ in Millions	3 Months Ended
	Mar. 31, 2018 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	(40)
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	284
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)	7.00%
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)	485.00%
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)	95.00%
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	(28.69)
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	928.16
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	$ 147
Derivative Financial Instruments, Liabilities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Liabilities, Fair Value Disclosure	483
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	254
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	8
Derivative Financial Instruments, Liabilities [Member] | Option Contracts, Power [Member] | Option Models [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Liabilities, Fair Value Disclosure	15
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	168
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	38
Derivative Financial Instruments, Assets [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	1,255
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	783
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	57
Derivative Financial Instruments, Assets [Member] | Option Contracts, Power [Member] | Option Models [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	49
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	100
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	$ 266