Fair Value Measurements (Significant Unobservable Inputs Used in Valuation of Contracts) (Details) - Jun. 30, 2015 - Level 3 [Member] - USD ($) $ / shares in Units, $ in Millions	Total
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	$ 1,218
Liabilities, Fair Value Disclosure	575
Forward Contracts - power [Member] | Discounted Cash Flow Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	561
Liabilities, Fair Value Disclosure	$ 180
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)	$ 2
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)	$ 135
Forward contracts - Gas [Member] | Discounted Cash Flow Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	$ 59
Liabilities, Fair Value Disclosure	$ 38
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)	$ 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)	$ 8
Forward contracts - other commodity related [Member] | Discounted Cash Flow Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	$ 13
Liabilities, Fair Value Disclosure	$ 5
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)	$ (32)
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)	$ 47
Options - Power [Member] | Option Models [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	$ 171
Liabilities, Fair Value Disclosure	$ 153
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)	2.00%
Options - Power [Member] | Option Models [Member] | Implied Volatilities [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected rates (as a percentage)	260.00%
Option Contracts, Primarily Gas [Member] | Option Models [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	$ 91
Liabilities, Fair Value Disclosure	$ 169
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)	97.00%
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)	$ (21)
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)	$ 158
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	$ 99