Income Taxes (Details 2) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Deferred tax liabilities:
Plant-related basis differences	$ (7,349,990)	$ (6,572,627)
Net regulatory assets/(liabilities)	(430,807)	(449,266)
Power purchase agreements	(17,138)	(265,429)
Nuclear decommissioning trusts	(553,558)	(439,481)
Other	(686,006)	(679,302)
Total	(9,037,499)	(8,406,105)
Deferred tax assets:
Accumulated deferred investment tax credit	108,338	111,170
Pension and other post-employment benefits	315,134	161,730
Nuclear decommissioning liabilities	612,945	285,889
Sale and leaseback	217,430	256,157
Provision for regulatory adjustments	97,607	100,504
Provision for contingencies	28,504	28,554
Unbilled/deferred revenues	12,217	18,642
Customer deposits	14,825	15,724
Net operating loss carryforwards	253,518	123,710
Capital losses	12,995	56,602
Other	96,676	19,009
Valuation allowance	(85,615)	(70,089)
Total	1,684,574	1,107,602
Noncurrent accrued taxes (including unrecognized tax benefits)	(814,597)	(1,261,455)
Accumulated deferred income taxes and taxes accrued	$ (8,167,522)	$ (8,559,958)