Fair Value Measurements (Significant Unobservable Inputs Used in Valuation of Contracts) (Details) - Level 3 [Member] $ / shares in Units, $ in Millions	9 Months Ended
	Sep. 30, 2015 USD ($) $ / shares
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	$ 1,170
Liabilities, Fair Value Disclosure	509
Forward Contracts - power [Member] | Discounted Cash Flow Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	640
Liabilities, Fair Value Disclosure	$ 218
Forward Contracts - Power [Member] | Discounted Cash Flow Member] | Forward Price [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected rates (in dollars per unit) | $ / shares	$ 7
Forward Contracts - Power [Member] | Discounted Cash Flow Member] | Forward Price [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected rates (in dollars per unit) | $ / shares	$ 125
Forward contracts - Gas [Member] | Discounted Cash Flow Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	$ 16
Liabilities, Fair Value Disclosure	$ 23
Forward contracts - Gas [Member] | Discounted Cash Flow Member] | Forward Price [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected rates (in dollars per unit) | $ / shares	$ 1
Forward contracts - Gas [Member] | Discounted Cash Flow Member] | Forward Price [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected rates (in dollars per unit) | $ / shares	$ 6
Forward contracts - other commodity related [Member] | Discounted Cash Flow Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	$ 12
Liabilities, Fair Value Disclosure	$ 1
Forward contracts - other commodity related [Member] | Discounted Cash Flow Member] | Forward Price [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected rates (in dollars per unit) | $ / shares	$ (29)
Forward contracts - other commodity related [Member] | Discounted Cash Flow Member] | Forward Price [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected rates (in dollars per unit) | $ / shares	$ 59
Options - Power [Member] | Option Models [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	$ 84
Liabilities, Fair Value Disclosure	$ 71
Options - Power [Member] | Option Models [Member] | Implied Correlations [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected rates (as a percentage)	(4.00%)
Options - Power [Member] | Option Models [Member] | Implied Correlations [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected rates (as a percentage)	99.00%
Options - Power [Member] | Option Models [Member] | Implied Volatilities [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected rates (as a percentage)	1.00%
Options - Power [Member] | Option Models [Member] | Implied Volatilities [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected rates (as a percentage)	133.00%
Option Contracts, Primarily Gas [Member] | Option Models [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	$ 95
Liabilities, Fair Value Disclosure	$ 166
Option Contracts, Primarily Gas [Member] | Option Models [Member] | Implied Correlations [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected rates (as a percentage)	(4.00%)
Option Contracts, Primarily Gas [Member] | Option Models [Member] | Implied Correlations [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected rates (as a percentage)	99.00%
Option Contracts, Primarily Gas [Member] | Option Models [Member] | Implied Volatilities [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected rates (as a percentage)	1.00%
Option Contracts, Primarily Gas [Member] | Option Models [Member] | Implied Volatilities [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected rates (as a percentage)	117.00%
Full Requirements and Unit Contingent Contracts [Member] | Discounted Cash Flow Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	$ 323
Liabilities, Fair Value Disclosure	$ 30
Full Requirements and Unit Contingent Contracts [Member] | Discounted Cash Flow Member] | Forward Price [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected rates (in dollars per unit) | $ / shares	$ (20)
Full Requirements and Unit Contingent Contracts [Member] | Discounted Cash Flow Member] | Forward Price [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected rates (in dollars per unit) | $ / shares	$ 156
Full Requirements and Unit Contingent Contracts [Member] | Discounted Cash Flow Member] | Customer Migration Rate [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected rates (as a percentage)	0.00%
Full Requirements and Unit Contingent Contracts [Member] | Discounted Cash Flow Member] | Customer Migration Rate [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected rates (as a percentage)	20.00%
NextEra Energy Resources [Member] | Interest rate contracts [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Liabilities, Fair Value Disclosure	$ 115