Significant Accounting Policy Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (151,100)	$ (325,117)
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax	(272,621)	(367,610)
Other Comprehensive Income (Loss), Net of Tax	174,017	422,225	54,212
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax	121,521	42,493
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	181,757
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(7,740)
Postretirement Benefit Costs [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Net of Tax	94,989
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	84,441
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	10,548
Cash Flow Hedging [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Net of Tax	79,028
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	97,316
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	$ (18,288)