CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Comprehensive income:
Net income	$ 183,060	$ 158,762	$ 366,953	$ 362,331
Pension and retiree medical benefits:
Amortization of losses included in net periodic benefit cost, net of tax of $647, $525, $1,269 and $1,076, respectively	932	754	1,827	1,548
Derivative instruments:
Net fair value (decrease) increase, net of tax of $(23,164), $(40), $(6,673) and $105, respectively	(35,727)	(38)	(10,335)	206
Reclassification of losses to net income, net of tax of $158, $140, $314 and $287, respectively	182	148	363	306
Total derivative instruments, net of tax	(35,545)	110	(9,972)	512
Marketable securities:
Net fair value increase, net of tax of $83, $0, $119 and $35, respectively	122	0	174	50
Other comprehensive (loss) income	(34,491)	864	(7,971)	2,110
Comprehensive income	$ 148,569	$ 159,626	$ 358,982	$ 364,441