Decommissioning Trust Funds (Securities Held) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Fair Value	$ 4,039,000	$ 3,788,000
Total Unrealized Gains	734,000	538,000
Total Unrealized Losses	7,000	19,000
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	2,370,000	2,129,000
Total Unrealized Gains	633,000	423,000
Total Unrealized Losses	1,000	14,000
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,669,000	1,659,000
Total Unrealized Gains	101,000	115,000
Total Unrealized Losses	$ 6,000	$ 5,000