CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Comprehensive income:
Net income	$ 236,570	$ 183,893
Pension and retiree medical benefits:
Amortization of (gains) losses included in net periodic benefit cost, net of tax of $2,503 and $622, respectively	(639)	895
Derivative instruments:
Net fair value increase, net of tax of $12 and $16,491, respectively	13	25,392
Reclassification of (gains) losses to net income, net of tax of $1,429 and $156, respectively	(305)	181
Total derivative instruments, net of tax	(292)	25,573
Marketable securities:
Net fair value (decrease) increase, net of tax of $(18) and $36, respectively	(36)	52
Other comprehensive (loss) income	(967)	26,520
Comprehensive income	$ 235,603	$ 210,413