Financial Instruments and Risk Management (Derivative Instruments by Income Statement Location) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Tax	$ 40,720,000	$ 41,399,000	$ 19,491,000
Deferred net gains (losses) on derivative instruments recoreded in AOCI, net of tax, expected to be reclasses during next 12 months	(32,700,000)
Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Net gain recognized in OCI on derivative (effective portion), net of tax of $40.7 million, $41.4 million and $19.5 million	66,438,000	67,547,000	31,801,000
Designated as Hedging Instrument | Operating revenues
Derivative Instruments, Gain (Loss) [Line Items]
Gain reclassified from accumulated OCI into income (effective portion)	52,694,000	26,326,000	200,324,000
Gain (loss) recognized in income on derivative (ineffective portion and amount excluded from effectiveness testing)	(5,340,000)	(2,767,000)	1,082,000
Not Designated as Hedging Instrument | Operating revenues
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) recognized in income on derivative	$ 61,841,000	$ (37,587,000)	$ (3,000)