Fair Value Measurements (Significant Unobservable Inputs) (Details) (Significant Unobservable Inputs (Level 3) [Member], USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	$ 1,069
Liabilities, Fair Value Disclosure	354
Forward Contracts - Power [Member] | Discounted Cash Flow Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	677
Liabilities, Fair Value Disclosure	74
Forward Contracts - Power [Member] | Foward Price [Member] | Maximum [Member] | Discounted Cash Flow Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Offered Quotes	$ 207
Forward Contracts - Power [Member] | Foward Price [Member] | Minimum [Member] | Discounted Cash Flow Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Offered Quotes	$ 13
Forward contracts - Gas [Member] | Discounted Cash Flow Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	82
Liabilities, Fair Value Disclosure	23
Forward contracts - Gas [Member] | Foward Price [Member] | Maximum [Member] | Discounted Cash Flow Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Offered Quotes	$ 16
Forward contracts - Gas [Member] | Foward Price [Member] | Minimum [Member] | Discounted Cash Flow Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Offered Quotes	$ 2
Forward contracts - Other [Member] | Discounted Cash Flow Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	15
Liabilities, Fair Value Disclosure	11
Forward contracts - Other [Member] | Foward Price [Member] | Maximum [Member] | Discounted Cash Flow Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Offered Quotes	$ 245
Forward contracts - Other [Member] | Foward Price [Member] | Minimum [Member] | Discounted Cash Flow Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Offered Quotes	$ 1
Options - gas [Member] | Options Models, Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	22
Liabilities, Fair Value Disclosure	29
Options - gas [Member] | Implied Volatilities [Member] | Maximum [Member] | Options Models, Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Expected Rates	175.00%
Options - gas [Member] | Implied Volatilities [Member] | Minimum [Member] | Options Models, Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Expected Rates	1.00%
Options - gas [Member] | Implied Correlations [Member] | Maximum [Member] | Options Models, Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Expected Rates	96.00%
Options - gas [Member] | Implied Correlations [Member] | Minimum [Member] | Options Models, Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Expected Rates	7.00%
Full Requirements and Unit Contingent Contracts [Member] | Discounted Cash Flow Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	218
Liabilities, Fair Value Disclosure	168
Full Requirements and Unit Contingent Contracts [Member] | Customer Migration Rate [Member] | Maximum [Member] | Discounted Cash Flow Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Expected Rates	20.00%	[1]
Full Requirements and Unit Contingent Contracts [Member] | Customer Migration Rate [Member] | Minimum [Member] | Discounted Cash Flow Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Expected Rates	0.00%	[1]
Full Requirements and Unit Contingent Contracts [Member] | Foward Price [Member] | Maximum [Member] | Discounted Cash Flow Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Offered Quotes	$ 222
Full Requirements and Unit Contingent Contracts [Member] | Foward Price [Member] | Minimum [Member] | Discounted Cash Flow Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Offered Quotes	$ (32)
Option Contracts, Power [Member] | Options Models, Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	55
Liabilities, Fair Value Disclosure	49
Option Contracts, Power [Member] | Implied Volatilities [Member] | Maximum [Member] | Options Models, Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Expected Rates	200.00%
Option Contracts, Power [Member] | Implied Volatilities [Member] | Minimum [Member] | Options Models, Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Expected Rates	1.00%
Option Contracts, Power [Member] | Implied Correlations [Member] | Maximum [Member] | Options Models, Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Expected Rates	96.00%
Option Contracts, Power [Member] | Implied Correlations [Member] | Minimum [Member] | Options Models, Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Expected Rates	7.00%
NEER [Member] | Interest Rate Swap [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Liabilities, Fair Value Disclosure	$ 93

[1] (a)Applies only to full requirements contracts.