Fair Value (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 59	$ 116
Nuclear decommissioning trusts	1,083	1,037
Other investments	116	108
Derivative assets - FTRs	1	1
Derivative Assets	1,259	1,262
Current	60	117
Noncurrent	1,199	1,145
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Nuclear decommissioning trusts	743	694
Other investments	68	64
Derivative assets - FTRs	0	0
Derivative Assets	811	758
Current	0	0
Noncurrent	811	758
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	59	116
Nuclear decommissioning trusts	340	343
Other investments	48	44
Derivative assets - FTRs	0	0
Derivative Assets	447	503
Current	59	116
Noncurrent	388	387
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Nuclear decommissioning trusts	0	0
Other investments	0	0
Derivative assets - FTRs	1	1
Derivative Assets	1	1
Current	1	1
Noncurrent	$ 0	$ 0