Long-term Debt and Capital Lease Obligations Schedule of Long-term Debt (Details) (USD $)	12 Months Ended																															1 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 First Mortgage Bonds, 5.0% to 8.7%, due through 2018 [Member]	Dec. 31, 2012 First Mortgage Bonds, 5.0% to 8.7%, due through 2018 [Member]	Dec. 31, 2013 First Mortgage Bonds, 3.0% to 8.5%, due 2019 to 2023 [Member]	Dec. 31, 2012 First Mortgage Bonds, 3.0% to 8.5%, due 2019 to 2023 [Member]	Dec. 31, 2013 First Mortgage Bonds, 6.7% due 2026 [Member]	Dec. 31, 2012 First Mortgage Bonds, 6.7% due 2026 [Member]	Dec. 31, 2013 First Mortgage Bonds, 7.7% due 2031 [Member]	Dec. 31, 2012 First Mortgage Bonds, 7.7% due 2031 [Member]	Dec. 31, 2013 First Mortgage Bonds, 5.3% to 6.4%, due 2034 to 2038 [Member]	Dec. 31, 2012 First Mortgage Bonds, 5.3% to 6.4%, due 2034 to 2038 [Member]	Dec. 31, 2013 First Mortgage Bonds, 4.1% to 6.0%, due 2039 to 2042 [Member]	Dec. 31, 2012 First Mortgage Bonds, 4.1% to 6.0%, due 2039 to 2042 [Member]	Dec. 31, 2013 Tax-exempt bond obligations, variable rate, due 2013 [Member]		Dec. 31, 2012 Tax-exempt bond obligations, variable rate, due 2013 [Member]		Dec. 31, 2013 Tax-exempt bond obligations, variable rate, due 2014 to 2025 [Member]		Dec. 31, 2012 Tax-exempt bond obligations, variable rate, due 2014 to 2025 [Member]		Dec. 31, 2013 Tax-exempt bond obligations, variable rate, due 2016 to 2024 [Member]		Dec. 31, 2012 Tax-exempt bond obligations, variable rate, due 2016 to 2024 [Member]		Dec. 31, 2013 Tax-exempt bond obligations, variable rate series, due 2014 to 2025 [Member]		Jun. 30, 2013 Tax-exempt bond obligations, variable rate series, due 2014 to 2025 [Member]	Dec. 31, 2012 Tax-exempt bond obligations, variable rate series, due 2014 to 2025 [Member]		Jun. 30, 2013 First Mortgage Bonds, 2.95%, Due June 2023 [Member]	Dec. 31, 2013 Long-term Debt [Member]	Dec. 31, 2012 Long-term Debt [Member]	Dec. 31, 2013 Capital Lease Obligations, 8.75% To 14.61%, Due Through 2036 [Member]	Dec. 31, 2012 Capital Lease Obligations, 8.75% To 14.61%, Due Through 2036 [Member]	Dec. 31, 2013 Minimum [Member] First Mortgage Bonds, 5.0% to 8.7%, due through 2018 [Member]	Dec. 31, 2012 Minimum [Member] First Mortgage Bonds, 5.0% to 8.7%, due through 2018 [Member]	Dec. 31, 2013 Minimum [Member] First Mortgage Bonds, 3.0% to 8.5%, due 2019 to 2023 [Member]	Dec. 31, 2012 Minimum [Member] First Mortgage Bonds, 3.0% to 8.5%, due 2019 to 2023 [Member]	Dec. 31, 2013 Minimum [Member] First Mortgage Bonds, 5.3% to 6.4%, due 2034 to 2038 [Member]	Dec. 31, 2012 Minimum [Member] First Mortgage Bonds, 5.3% to 6.4%, due 2034 to 2038 [Member]	Dec. 31, 2013 Minimum [Member] First Mortgage Bonds, 4.1% to 6.0%, due 2039 to 2042 [Member]	Dec. 31, 2012 Minimum [Member] First Mortgage Bonds, 4.1% to 6.0%, due 2039 to 2042 [Member]	Dec. 31, 2012 Minimum [Member] Tax-exempt bond obligations, variable rate series, due 2014 to 2025 [Member]	Dec. 31, 2013 Minimum [Member] Capital Lease Obligations, 8.75% To 14.61%, Due Through 2036 [Member]	Dec. 31, 2012 Minimum [Member] Capital Lease Obligations, 8.75% To 14.61%, Due Through 2036 [Member]	Dec. 31, 2013 Maximum [Member] First Mortgage Bonds, 5.0% to 8.7%, due through 2018 [Member]	Dec. 31, 2012 Maximum [Member] First Mortgage Bonds, 5.0% to 8.7%, due through 2018 [Member]	Dec. 31, 2013 Maximum [Member] First Mortgage Bonds, 3.0% to 8.5%, due 2019 to 2023 [Member]	Dec. 31, 2012 Maximum [Member] First Mortgage Bonds, 3.0% to 8.5%, due 2019 to 2023 [Member]	Dec. 31, 2013 Maximum [Member] First Mortgage Bonds, 5.3% to 6.4%, due 2034 to 2038 [Member]	Dec. 31, 2012 Maximum [Member] First Mortgage Bonds, 5.3% to 6.4%, due 2034 to 2038 [Member]	Dec. 31, 2013 Maximum [Member] First Mortgage Bonds, 4.1% to 6.0%, due 2039 to 2042 [Member]	Dec. 31, 2012 Maximum [Member] First Mortgage Bonds, 4.1% to 6.0%, due 2039 to 2042 [Member]	Dec. 31, 2012 Maximum [Member] Tax-exempt bond obligations, variable rate series, due 2014 to 2025 [Member]	Dec. 31, 2013 Maximum [Member] Capital Lease Obligations, 8.75% To 14.61%, Due Through 2036 [Member]	Dec. 31, 2012 Maximum [Member] Capital Lease Obligations, 8.75% To 14.61%, Due Through 2036 [Member]	Dec. 31, 2013 Letters of credit supporting tax-exempt bond obligations [Member]	Dec. 31, 2012 Letters of credit supporting tax-exempt bond obligations [Member]
Debt Instrument [Line Items]
Letters of Credit Outstanding, Amount																																																											$ 559,000,000	$ 601,000,000
Principal Amount			721,000,000		1,824,000,000		100,000,000		300,000,000		2,350,000,000		950,000,000		0	[1],[2]			325,000,000	[2]			221,000,000	[1],[2]			51,000,000	[1],[3]	51,000,000			300,000,000	6,842,000,000
Carrying Value	6,828,000,000	6,806,000,000	721,000,000	941,000,000	1,821,000,000	1,522,000,000	100,000,000	100,000,000	299,000,000	299,000,000	2,346,000,000	2,346,000,000	944,000,000	943,000,000	0	[1],[2]	41,000,000	[1],[2]	325,000,000	[2]	325,000,000	[2]	221,000,000	[1],[2]	221,000,000	[1],[2]	51,000,000	[1],[3]		68,000,000	[1],[3]		6,828,000,000	6,806,000,000
Average Interest Rate			5.50%	5.60%	4.50%	4.80%	6.70%	6.70%	7.70%	7.70%	6.00%	6.00%	5.40%	5.40%	0.00%	[1],[2]	0.14%	[1],[2]	0.17%	[2]	0.15%	[2]	0.06%	[1],[2]	0.15%	[1],[2]	0.22%	[1],[3]		4.02%	[1],[3]				11.47%	11.30%
Capital Lease Obligations																																			49,000,000	55,000,000
Long-term Debt and Capital Lease Obligations, Principal Amount	6,891,000,000
Total long-term debt and capital lease obligations	6,877,000,000	6,861,000,000
Current portion of long-term debt and capital lease obligations	238,000,000	267,000,000
Long-term debt and capital lease obligations	6,639,000,000	6,594,000,000
Debt Instrument, Interest Rate, Stated Percentage							6.70%	6.70%	7.70%	7.70%																						2.95%					5.00%	5.00%	3.00%	3.00%	5.30%	5.30%	4.10%	4.10%	3.90%	8.75%	8.75%	8.70%	8.70%	8.50%	8.50%	6.40%	6.40%	6.00%	6.00%	4.13%	14.61%	14.61%
Debt Instrument, Maturity Date																																Jun. 30, 2023
Debt Instrument, Repurchased Face Amount																													17,000,000
Maximum amount of additional long-term debt approved by regulators	550,000,000
Eligible Property Subject To Lien Of Mortgages	24,000,000,000
Capital Leases, Balance Sheet, Assets by Major Class, Net	$ 49,000,000	$ 55,000,000

[1] Secured by pledged first mortgage bonds registered to and held by the tax-exempt bond trustee generally with the same interest rates, maturity dates and redemption provisions as the tax-exempt bond obligations.

[2] Supported by $559 million and $601 million of fully available letters of credit issued under committed bank arrangements as of December 31, 2013 and 2012, respectively.

[3] Interest rates were fixed at 3.90% to 4.13% as of December 31, 2012 and were scheduled to reset to variable or fixed in June 2013. In June 2013, $17 million of these tax-exempt bond obligations were redeemed and retired prior to their scheduled 2014 maturity date. The interest rates for the remaining $51 million were reset to variable interest rates.