Retirement, Other Postretirement Benefits, and Defined Contribution Plans (Details 1) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Change in Projected Benefit Obligation
Service cost	$ 59,340	$ 52,313	$ 46,765
Interest cost	74,522	76,078	75,265
Early Retiree Reinsurance Program proceeds	3,348
Amount recognized in the balance sheet
Current liabilities	44,031	39,862
Defined benefit pension plan liability	3,133,657	2,175,364
Total Funded Status - Other Postretirement Benefit Plan	(1,225,197)	(981,940)
Amount recognized as AOCI (before tax)
Prior service cost	2,648	2,855
Net loss	551,613	297,093
Total	554,261	299,948
Qualified Pension [Member]
Change in Projected Benefit Obligation
Balance at beginning of year	4,301,218	3,837,744
Service cost	121,961	104,956	89,646
Interest cost	236,992	231,206	218,172
Actuarial loss	703,895	293,189
Plan participant contributions	828	894
Benefits paid	(177,259)	(166,771)
Balance at end of year	5,187,635	4,301,218	3,837,744
Change in Plan Assets
Fair value of assets at beginning of year	3,216,268	2,607,274
Actual return on plan assets	(40,453)	320,517
Employer contributions	400,532	454,354
Plan participant contributions	828	894
Benefits paid	(177,259)	(166,771)
Fair value of assets at end of year	3,399,916	3,216,268	2,607,274
Funded status	(1,787,719)	(1,084,950)
Amount recognized in the balance sheet
Defined benefit pension plan liability	(1,787,719)	(1,084,950)
Amount recognized as a regulatory asset
Prior service cost	9,836	12,979
Net loss	2,048,743	1,350,616
Total Regulatory Asset	2,058,579	1,363,595
Other Postretirement Trusts [Member]
Change in Projected Benefit Obligation
Balance at beginning of year	1,386,370	1,280,076
Service cost	59,340	52,313
Interest cost	74,522	76,078
Plan amendments	(29,507)	(50,548)
Actuarial loss	216,549	92,340
Plan participant contributions	14,650	14,275
Benefits paid	(77,454)	(83,613)
Medicare Part D subsidy received	4,551	5,449
Balance at end of year	1,652,369	1,386,370
Change in Plan Assets
Fair value of assets at beginning of year	404,430	362,399
Actual return on plan assets	9,432	36,364
Employer contributions	76,114	75,005
Plan participant contributions	14,650	14,275
Benefits paid	(77,454)	(83,613)
Fair value of assets at end of year	427,172	404,430
Funded status	(1,225,197)	(981,940)
Amount recognized in the balance sheet
Current liabilities	(32,832)	(30,225)
Defined benefit pension plan liability	(1,192,365)	(951,715)
Amount recognized as a regulatory asset
Transition obligation	2,557	5,118
Prior service cost	(6,628)	(8,442)
Net loss	353,905	253,415
Total Regulatory Asset	349,834	250,091
Amount recognized as AOCI (before tax)
Transition obligation	620	1,242
Prior service cost	(66,176)	(48,925)
Net loss	313,379	198,466
Total	$ 247,823	$ 150,783