Fair Value (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 106	$ 116
Nuclear decommissioning trusts	1,080	1,037
Other investments	117	108
Derivative assets - FTRs	2	1
Assets, Fair Value Disclosure, Recurring	1,305	1,262
Current	108	117
Noncurrent	1,197	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	749	694
Other investments	70	64
Derivative assets - FTRs	0	0
Assets, Fair Value Disclosure, Recurring	819	758
Current	0	0
Noncurrent	819	758
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	106	116
Nuclear decommissioning trusts	331	343
Other investments	47	44
Derivative assets - FTRs	0	0
Assets, Fair Value Disclosure, Recurring	484	503
Current	106	116
Noncurrent	378	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	2	1
Assets, Fair Value Disclosure, Recurring	2	1
Current	2	1
Noncurrent	$ 0	$ 0