CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Comprehensive income:
Net income	$ 183,893	$ 203,569
Pension and retiree medical benefits:
Amortization of losses included in net periodic benefit cost, net of tax of $622 and $551, respectively	895	794
Derivative instruments:
Net fair value increase, net of tax of $16,491 and $147, respectively	25,392	244
Reclassification of losses to net income, net of tax of $156 and $147, respectively	181	158
Total derivative instruments, net of tax	25,573	402
Marketable securities:
Net fair value increase, net of tax of $36 and $34, respectively	52	50
Other comprehensive income	26,520	1,246
Comprehensive income	$ 210,413	$ 204,815