Fair Value Measurements (Significant Unobservable Inputs Used in Valuation of Contracts) (Details) (Level 3 [Member], USD $) In Millions, except Per Share data, unless otherwise specified	9 Months Ended
	Sep. 30, 2013
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	$ 937
Liabilities, Fair Value Disclosure	222
Forward Contracts - power [Member] | Discounted Cash Flow Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	507
Liabilities, Fair Value Disclosure	67
Forward Contracts - power [Member] | Discounted Cash Flow Member] | Foward Price [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected rates (in dollars per unit)	$ 10
Forward Contracts - power [Member] | Discounted Cash Flow Member] | Foward Price [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected rates (in dollars per unit)	$ 205
Forward contracts - Gas [Member] | Discounted Cash Flow Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	53
Liabilities, Fair Value Disclosure	12
Forward contracts - Gas [Member] | Discounted Cash Flow Member] | Foward Price [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected rates (in dollars per unit)	$ 2
Forward contracts - Gas [Member] | Discounted Cash Flow Member] | Foward Price [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected rates (in dollars per unit)	$ 4
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	14
Forward contracts - other commodity related [Member] | Discounted Cash Flow Member] | Foward Price [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected rates (in dollars per unit)	$ 1
Forward contracts - other commodity related [Member] | Discounted Cash Flow Member] | Foward Price [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected rates (in dollars per unit)	$ 245
Options - Power [Member] | Option Models [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	106
Liabilities, Fair Value Disclosure	63
Options - Power [Member] | Option Models [Member] | Implied Correlations [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected rates (as a percentage)	7.00%
Options - Power [Member] | Option Models [Member] | Implied Correlations [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected rates (as a percentage)	96.00%
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)	111.00%
Options - Gas [Member] | Option Models [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	25
Liabilities, Fair Value Disclosure	16
Options - Gas [Member] | Option Models [Member] | Implied Correlations [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected rates (as a percentage)	7.00%
Options - Gas [Member] | Option Models [Member] | Implied Correlations [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected rates (as a percentage)	96.00%
Options - 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%
Options - Gas [Member] | Option Models [Member] | Implied Volatilities [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected rates (as a percentage)	36.00%
Full Requirements and Unit Contingent Contracts [Member] | Discounted Cash Flow Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	234
Liabilities, Fair Value Disclosure	50
Full Requirements and Unit Contingent Contracts [Member] | Discounted Cash Flow Member] | Foward Price [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected rates (in dollars per unit)	$ (32)
Full Requirements and Unit Contingent Contracts [Member] | Discounted Cash Flow Member] | Foward Price [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected rates (in dollars per unit)	$ 136
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	$ 91