Consolidated Statements Of Comprehensive Income - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Net income		$ 207,123	$ 250,972	$ 177,391	$ 183,636	$ 252,085	$ 198,620	$ 146,260	$ 242,554	$ 819,122	$ 839,519	$ 582,237
Other comprehensive income:
Net loss on cash flow hedges(1)	[1]									(14,904)	(30,090)	(4,744)
Reclassification of net loss (gain) on cash flow hedges to income(1)	[1]									1,365	(124)	4,245
Net actuarial (loss) gain(2)	[2]									(8,359)	(33,937)	14,089
Plan amendment(2)	[2]									3,610	0	0
Amortization of prior service credit(2)	[2]									(3,713)	(3,680)	(3,405)
Amortization of actuarial loss(2)	[2]									7,191	3,986	5,369
Settlement cost(2)	[2]									0	1,809	0
Total other comprehensive income (loss)										(14,810)	(62,036)	15,554
Comprehensive income										$ 804,312	$ 777,483	$ 597,791

[1] See Note 13–Derivative Financial Instruments for details of the amount of gain/loss recognized in accumulated other comprehensive loss ("AOCL") on derivatives and the amount of gain/loss reclassified from AOCL into income.

[2] See Note 10–Employee Benefit Plans for additional detail of the changes in employee benefit plan assets and benefit obligations that are recognized in other comprehensive income (loss).