Retirement and Other Postretirement Benefits (Details) (USD $) In Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Qualified Pension [Member]
Components of Qualified Net Pension Cost and Net Other Postretirement Benefit Cost and Other Amounts Recognized as a Regulatory Asset and/or Accumulated Other Comprehensive Income (AOCI)
Service cost - benefits earned during the period	$ 30,490	$ 26,239	$ 91,470	$ 78,717
Interest cost on accumulated postretirement benefit obligation (APBO)	59,248	57,802	177,744	173,406
Expected return on assets	(75,319)	(64,902)	(225,957)	(194,706)
Amortization of prior service cost (credit)	838	1,164	2,514	3,492
Amortization of loss	23,244	16,475	69,732	49,425
Net other postretirement benefit cost	38,501	36,778	115,503	110,334
Other Postretirement [Member]
Components of Qualified Net Pension Cost and Net Other Postretirement Benefit Cost and Other Amounts Recognized as a Regulatory Asset and/or Accumulated Other Comprehensive Income (AOCI)
Service cost - benefits earned during the period	14,835	13,078	44,505	39,234
Interest cost on accumulated postretirement benefit obligation (APBO)	18,631	19,020	55,893	57,060
Expected return on assets	(7,369)	(6,553)	(22,107)	(19,659)
Amortization of transition obligation	796	932	2,388	2,796
Amortization of prior service cost (credit)	(3,518)	(3,015)	(10,554)	(9,045)
Amortization of loss	5,298	4,317	15,894	12,951
Net other postretirement benefit cost	$ 28,673	$ 27,779	$ 86,019	$ 83,337