Supplemental Guarantor Condensed Financial Information (Condensed Consolidating Statements of Income (Loss)) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Condensed Financial Statements, Captions [Line Items]
Operating revenues	$ 1,893	$ 1,752	$ 4,572	$ 4,358
Fuel, purchased power costs and delivery fees	(852)	(850)	(2,175)	(2,153)
Net gain from commodity hedging and trading activities	58	(3)	29	229
Operating costs	(189)	(201)	(685)	(636)
Depreciation and amortization	(331)	(328)	(1,012)	(992)
Selling, general and administrative expenses	(175)	(174)	(502)	(484)
Franchise and revenue-based taxes	(18)	(19)	(51)	(55)
Other income	1	2	7	12
Other deductions	(8)	(30)	(12)	(37)
Interest income	1	10	5	36
Interest expense and related charges	(340)	(772)	(1,338)	(2,268)
Income (loss) before income taxes	40	(613)	(1,162)	(1,990)
Income tax (expense) benefit	17	228	476	692
Equity earnings of subsidiaries	0	0	0	0
Net income (loss)	57	(385)	(686)	(1,298)
Other comprehensive income	1	1	5	5
Comprehensive income (loss)	58	(384)	(681)	(1,293)
Parent/ Guarantor [Member]
Condensed Financial Statements, Captions [Line Items]
Operating revenues	0	0	0	0
Fuel, purchased power costs and delivery fees	0	0	0	0
Net gain from commodity hedging and trading activities	0	0	0	0
Operating costs	0	0	0	0
Depreciation and amortization	0	0	0	0
Selling, general and administrative expenses	0	0	0	0
Franchise and revenue-based taxes	0	0	0	0
Other income	0	0	0	0
Other deductions	0	0	0	0
Interest income	0	0	1	0
Interest expense and related charges	(4)	(24)	(15)	(69)
Income (loss) before income taxes	(4)	(24)	(14)	(69)
Income tax (expense) benefit	1	8	7	23
Equity earnings of subsidiaries	60	(369)	(679)	(1,252)
Net income (loss)	57	(385)	(686)	(1,298)
Other comprehensive income	1	1	5	5
Comprehensive income (loss)	58	(384)	(681)	(1,293)
Issuer [Member]
Condensed Financial Statements, Captions [Line Items]
Operating revenues	0	0	0	0
Fuel, purchased power costs and delivery fees	0	0	0	0
Net gain from commodity hedging and trading activities	20	(98)	(3)	173
Operating costs	0	0	0	0
Depreciation and amortization	0	0	0	0
Selling, general and administrative expenses	(14)	(4)	(49)	(4)
Franchise and revenue-based taxes	0	0	0	0
Other income	0	0	0	6
Other deductions	0	0	0	0
Interest income	62	91	182	242
Interest expense and related charges	(541)	(982)	(1,920)	(2,794)
Income (loss) before income taxes	(473)	(993)	(1,790)	(2,377)
Income tax (expense) benefit	165	347	630	829
Equity earnings of subsidiaries	368	277	481	296
Net income (loss)	60	(369)	(679)	(1,252)
Other comprehensive income	1	1	5	5
Comprehensive income (loss)	61	(368)	(674)	(1,247)
Other Guarantors [Member]
Condensed Financial Statements, Captions [Line Items]
Operating revenues	1,893	1,752	4,572	4,358
Fuel, purchased power costs and delivery fees	(852)	(850)	(2,175)	(2,153)
Net gain from commodity hedging and trading activities	38	95	32	56
Operating costs	(192)	(201)	(690)	(636)
Depreciation and amortization	(332)	(328)	(1,011)	(992)
Selling, general and administrative expenses	(173)	(172)	(481)	(486)
Franchise and revenue-based taxes	(18)	(19)	(51)	(55)
Other income	1	2	7	6
Other deductions	(8)	(30)	(12)	(36)
Interest income	206	232	591	593
Interest expense and related charges	(619)	(606)	(1,842)	(1,778)
Income (loss) before income taxes	(56)	(125)	(1,060)	(1,123)
Income tax (expense) benefit	46	54	420	379
Equity earnings of subsidiaries	1	0	1	0
Net income (loss)	(9)	(71)	(639)	(744)
Other comprehensive income	0	0	0	0
Comprehensive income (loss)	(9)	(71)	(639)	(744)
Non-guarantors [Member]
Condensed Financial Statements, Captions [Line Items]
Operating revenues	27	3	59	8
Fuel, purchased power costs and delivery fees	0	0	0	0
Net gain from commodity hedging and trading activities	0	0	0	0
Operating costs	0	0	0	0
Depreciation and amortization	1	0	(1)	0
Selling, general and administrative expenses	(11)	(1)	(25)	(2)
Franchise and revenue-based taxes	0	0	0	0
Other income	0	0	0	0
Other deductions	0	0	0	(1)
Interest income	0	0	0	0
Interest expense and related charges	(4)	(2)	(8)	(5)
Income (loss) before income taxes	13	0	25	0
Income tax (expense) benefit	(5)	0	(9)	0
Equity earnings of subsidiaries	0	0	0	0
Net income (loss)	8	0	16	0
Other comprehensive income	0	0	0	0
Comprehensive income (loss)	8	0	16	0
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Operating revenues	(27)	(3)	(59)	(8)
Fuel, purchased power costs and delivery fees	0	0	0	0
Net gain from commodity hedging and trading activities	0	0	0	0
Operating costs	3	0	5	0
Depreciation and amortization	0	0	0	0
Selling, general and administrative expenses	23	3	53	8
Franchise and revenue-based taxes	0	0	0	0
Other income	0	0	0	0
Other deductions	0	0	0	0
Interest income	(267)	(313)	(769)	(799)
Interest expense and related charges	828	842	2,447	2,378
Income (loss) before income taxes	560	529	1,677	1,579
Income tax (expense) benefit	(190)	(181)	(572)	(539)
Equity earnings of subsidiaries	(429)	92	197	956
Net income (loss)	(59)	440	1,302	1,996
Other comprehensive income	(1)	(1)	(5)	(5)
Comprehensive income (loss)	$ (60)	$ 439	$ 1,297	$ 1,991