Fair Value Measurements (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Fair Value Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation
Estimated fair value of long-term debt	$ 3,000,000,000	$ 2,000,000,000
Derivative instruments, at fair value, net
Fair Value Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation
Balance at the beginning of the year	116,672,000	88,570,000
Total gains or losses included in earnings	14,000	(14,000)
Total gains or losses included in other comprehensive income	81,825,000	87,330,000
Settlements	(55,251,000)	(59,214,000)
Balance at the end of the year	143,260,000	116,672,000
Earnings attributable to the change in unrealized gains/losses		$ 5,000