Long-Term Debt (Debt Redemptions) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2014
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Amount	$ 837
March 2014 Mortgage Bonds Various Interest Rates Maturing in 2014 [Member] | Mortgages [Member]
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Amount	13
March 2014 Securitization Bonds 6.62% Maturing in 2014 [Member] | Securitization Bonds [Member]
Extinguishment of Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.62%
Extinguishment of Debt, Amount	100
April 2014 Tax Exempt Revenue Bonds 2.35% Maturing in 2024 [Member] | Tax Exempt Revenue Bonds [Member]
Extinguishment of Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.35%
Extinguishment of Debt, Amount	31
April 2014 Tax Exempt Revenue Bonds 4.65% Maturing in 2028 [Member] | Tax Exempt Revenue Bonds [Member]
Extinguishment of Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.65%
Extinguishment of Debt, Amount	32
June 2014 Tax Exempt Revenue Bonds 4.875% Maturing in 2029 [Member] | Tax Exempt Revenue Bonds [Member]
Extinguishment of Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.875%
Extinguishment of Debt, Amount	36
June 2014 Tax Exempt Revenue Bonds 6.00% Maturing in 2036 [Member] | Tax Exempt Revenue Bonds [Member]
Extinguishment of Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.00%
Extinguishment of Debt, Amount	69
July 2014 Senior Notes 4.80% Maturing in 2015 [Member] | Senior Notes [Member]
Extinguishment of Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.80%
Extinguishment of Debt, Amount	200
August 2014 Senior Notes 5.40% Maturing in 2014 [Member] | Senior Notes [Member]
Extinguishment of Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.40%
Extinguishment of Debt, Amount	200
August 2014 Tax Exempt Revenue Bonds 5.25% Maturing in 2029 [Member] | Tax Exempt Revenue Bonds [Member]
Extinguishment of Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.25%
Extinguishment of Debt, Amount	60
September 2014 Securitization Bonds 6.62% Maturing in 2014 [Member] | Securitization Bonds [Member]
Extinguishment of Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.62%
Extinguishment of Debt, Amount	$ 96