Retirement, Other Postretirement Benefits, and Defined Contribution Plans (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Other Postretirement Plan - Net Periodic Benefit Cost
Service cost - benefits earned during the period	$ 59,340	$ 52,313	$ 46,765
Interest cost on projected benefit obligation (PBO)	74,522	76,078	75,265
Expected return on assets	(29,477)	(26,213)	(23,484)
Amortization of transition obligation	3,183	3,728	3,732
Amortization of prior service cost (credit)	(14,070)	(12,060)	(16,096)
Recognized net loss	21,192	17,270	18,970
Net periodic benefit costs	114,690	111,116	105,152
Qualified Pension [Member]
Other Postretirement Plan - Net Periodic Benefit Cost
Service cost - benefits earned during the period	121,961	104,956	89,646
Interest cost on projected benefit obligation (PBO)	236,992	231,206	218,172
Expected return on assets	(301,276)	(259,608)	(249,220)
Amortization of prior service cost (credit)	3,350	4,658	4,997
Recognized net loss	92,977	65,901	22,401
Net periodic benefit costs	154,004	147,113	85,996
Other changes in plan assets and benefit obligations recognized as a regulatory asset and/or AOCI (after tax) Arising this period:
Net (gain)/loss	1,045,624	232,279	76,799
Amounts reclassified from regulatory asset and/or AOCI to net periodic pension cost the current year:
Amortization of prior service cost	(3,350)	(4,658)	(4,997)
Amortization of net loss	(92,977)	(65,901)	(22,401)
Total	949,297	161,720	49,401
Total recognized as net periodic pension cost, regulatory asset, and/or AOCI (before tax)	1,103,301	308,834	135,397
Estimated amortization amounts from regulatory asset and/or AOCI to net periodic cost in the following year
Prior service cost	2,733	3,350	4,658
Net loss	169,064	92,977	65,901
Other Postretirement Trusts [Member]
Other Postretirement Plan - Net Periodic Benefit Cost
Service cost - benefits earned during the period	59,340	52,313
Interest cost on projected benefit obligation (PBO)	74,522	76,078
Other changes in plan assets and benefit obligations recognized as a regulatory asset and/or AOCI (after tax) Arising this period:
Prior service credit for period	(29,507)	(50,548)	0
Net (gain)/loss	236,594	82,189	24,983
Amounts reclassified from regulatory asset and/or AOCI to net periodic pension cost the current year:
Amortization of transition obligation	(3,183)	(3,728)	(3,732)
Amortization of prior service cost	14,070	12,060	16,096
Amortization of net loss	(21,192)	(17,270)	(18,970)
Total	196,782	22,703	18,377
Total recognized as net periodic pension cost, regulatory asset, and/or AOCI (before tax)	311,472	133,819	123,529
Estimated amortization amounts from regulatory asset and/or AOCI to net periodic cost in the following year
Transition obligation	3,177	3,183	3,728
Prior service cost	(18,163)	(14,070)	(12,060)
Net loss	$ 43,127	$ 21,192	$ 17,270