Unaudited Quarterly Financial Information (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Information Disclosure [Abstract]
Net Operating Revenues	$ 4,645,497		$ 5,118,616		$ 4,187,556		$ 4,083,671		$ 3,749,023		$ 3,541,396		$ 3,840,185		$ 3,356,514		$ 18,035,340	$ 14,487,118	$ 11,682,636
Operating Income	1,226,652		1,786,162		1,144,730		1,084,279		980,324		769,769		1,092,044		833,074		5,241,823	3,675,211	1,479,797
Income Before Income Taxes	1,148,593		1,715,120		1,100,813		1,030,789		919,082		721,555		1,035,230		761,019		4,995,315	3,436,886	1,280,740
Income Tax Provision	704,005		611,502		394,460		369,861		338,888		259,057		375,538		266,294		2,079,828	1,239,777	710,461
Net Income	$ 444,588		$ 1,103,618		$ 706,353		$ 660,928		$ 580,194		$ 462,498		$ 659,692		$ 494,725		$ 2,915,487	$ 2,197,109	$ 570,279
Net Income Per Share
Basic (in dollars per share)	$ 0.82	[1]	$ 2.03	[1]	$ 1.30	[1]	$ 1.22	[1]	$ 1.07	[1]	$ 0.85	[1]	$ 1.22	[1]	$ 0.92	[1]	$ 5.36	$ 4.07	$ 1.07
Diluted (in dollars per share)	$ 0.81	[1]	$ 2.01	[1]	$ 1.29	[1]	$ 1.21	[1]	$ 1.06	[1]	$ 0.85	[1]	$ 1.21	[1]	$ 0.91	[1]	$ 5.32	$ 4.02	$ 1.05
Average Number of Common Shares [Abstract]
Basic (in shares)	544,579		543,984		543,099		542,278		541,857		540,941		540,033		538,717		543,443	540,341	535,155
Diluted (in shares)	549,153		549,518		548,676		548,071		547,966		547,152		545,477		544,526		548,539	546,227	541,524

[1] 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.