Unaudited Quarterly Financial Information (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Net Operating Revenues	$ 3,340,439		$ 2,644,844		$ 2,612,472		$ 2,610,565		$ 2,402,039		$ 2,118,504		$ 1,775,740		$ 1,354,349		$ 11,208,320	$ 7,650,632	$ 8,757,428
Operating Income	475,912		214,836		127,908		107,746		(105,487)		(193,480)		(288,173)		(638,141)		926,402	(1,225,281)	(6,686,079)
Income (Loss) Before Income Taxes	413,353		145,980		62,467		39,382		(194,010)		(272,250)		(380,277)		(710,968)
Income Tax Provision (Benefit)	(2,017,115)	[1]	45,439	[1]	39,414	[1]	10,865	[1]	(51,658)		(82,250)		(87,719)		(239,192)		(1,921,397)	(460,819)	(2,397,041)
Net Income (Loss)	$ 2,430,468		$ 100,541		$ 23,053		$ 28,517		$ (142,352)		$ (190,000)		$ (292,558)		$ (471,776)		$ 2,582,579	$ (1,096,686)	$ (4,524,515)
Net Income (Loss) Per Share
Basic (in dollars per share)	$ 4.22	[2]	$ 0.17	[2]	$ 0.04	[2]	$ 0.05	[2]	$ (0.25)	[2]	$ (0.35)	[2]	$ (0.53)	[2]	$ (0.86)	[2]	$ 4.49	$ (1.98)	$ (8.29)
Diluted (in dollars per share)	$ 4.20	[2]	$ 0.17	[2]	$ 0.04	[2]	$ 0.05	[2]	$ (0.25)	[2]	$ (0.35)	[2]	$ (0.53)	[2]	$ (0.86)	[2]	$ 4.46	$ (1.98)	$ (8.29)
Average Number of Common Shares [Abstract]
Basic (in shares)	575,394		574,783		574,439		573,935		567,337		547,838		547,335		546,715		574,620	553,384	545,697
Diluted	579,203		578,736		578,483		578,593		567,337		547,838		547,335		546,715		578,693	553,384	545,697
Provisional Reduction in the Income Tax Provision																	$ 2,200,000

[1] Includes an income tax benefit of approximately $2.2 billion for the quarter ended December 31, 2017, primarily due to the enactment of the Tax Cuts and Jobs Act in December 2017. See Note 6 to the Consolidated Financial Statements.

[2] The sum of quarterly net income (loss) per share may not agree with total year net income (loss) per share as each quarterly computation is based on the weighted average of common shares outstanding.