Fair Value (Reconciliation of Level 3 Assets and Liabilities at Fair Value on a Recurring Basis) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis
Beginning Balance	$ (43)	$ (41)	$ (36)	$ (13)
Transfers into Level 3	0	0	0	0
Transfer out of Level 3	0	0	0	(2)
Total gains (losses): [Abstract]
Included in earnings	(39)	15	(19)	15
Recorded in regulatory assets/liabilities	7	3	11	4
Purchases issuances and settlements [Abstract]
Purchases			0	1
Issuances	(1)	0	(2)	0
Settlements	36	7	6	(21)
Ending Balance	(40)	(16)	(40)	(16)
The amount of total gains (losses) included in net income attributed to the change in unrealized gains or losses related to assets still held at the end of the period	(10)	31	(30)	20
Natural Gas Commodity Contract [Member]
Fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis
Beginning Balance	(10)	(34)	(52)	(38)
Transfers into Level 3	0	0	0	0
Transfer out of Level 3	0	0	0	(2)
Total gains (losses): [Abstract]
Included in earnings	(16)	(2)	(38)	(10)
Recorded in regulatory assets/liabilities	0	0	0	0
Purchases issuances and settlements [Abstract]
Purchases			0	0
Issuances	0	0	0	0
Settlements	6	6	70	20
Ending Balance	(20)	(30)	(20)	(30)
The amount of total gains (losses) included in net income attributed to the change in unrealized gains or losses related to assets still held at the end of the period	(11)	(1)	(11)	(6)
Electricity Commodity Contract [Member]
Fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis
Beginning Balance	(34)	(9)	13	23
Transfers into Level 3	0	0	0	0
Transfer out of Level 3	0	0	0	0
Total gains (losses): [Abstract]
Included in earnings	(22)	18	20	26
Recorded in regulatory assets/liabilities	0	0	0	0
Purchases issuances and settlements [Abstract]
Purchases			0	1
Issuances	(1)	0	(2)	0
Settlements	30	3	(58)	(38)
Ending Balance	(27)	12	(27)	12
The amount of total gains (losses) included in net income attributed to the change in unrealized gains or losses related to assets still held at the end of the period	1	33	(19)	27
Other Commodity Contract [Member]
Fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis
Beginning Balance	1	2	3	2
Transfers into Level 3	0	0	0	0
Transfer out of Level 3	0	0	0	0
Total gains (losses): [Abstract]
Included in earnings	(1)	(1)	(1)	(1)
Recorded in regulatory assets/liabilities	7	3	11	4
Purchases issuances and settlements [Abstract]
Purchases			0	0
Issuances	0	0	0	0
Settlements	0	(2)	(6)	(3)
Ending Balance	7	2	7	2
The amount of total gains (losses) included in net income attributed to the change in unrealized gains or losses related to assets still held at the end of the period	$ 0	$ (1)	$ 0	$ (1)