Decommissioning Trust Funds (Available For Sale Securities Continuous Unrealized Loss Position Fair Value) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months Fair Value	$ 12,000	$ 130,000
More than 12 months Fair Value	24,000	43,000
Total Fair Value	36,000	173,000
Less than 12 Months Gross Unrealized Losses		9,000
More than 12 Months Gross Unrealized Losses	1,000	5,000
Total Gross Unrealized Losses	1,000	14,000
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months Fair Value	284,000	123,000
More than 12 months Fair Value	56,000	60,000
Total Fair Value	340,000	183,000
Less than 12 Months Gross Unrealized Losses	3,000	3,000
More than 12 Months Gross Unrealized Losses	3,000	2,000
Total Gross Unrealized Losses	$ 6,000	$ 5,000