Unaudited Quarterly Financial Information (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2019		Sep. 30, 2019		Jun. 30, 2019		Mar. 31, 2019		Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Operating Revenues and Other	$ 4,320,246		$ 4,303,455		$ 4,697,630		$ 4,058,642		$ 4,574,536		$ 4,781,624		$ 4,238,077		$ 3,681,162		$ 17,379,973	$ 17,275,399	$ 11,208,320
Operating Income	863,751		827,959		1,130,771		876,530		1,123,140		1,506,687		964,931		874,588		3,699,011	4,469,346	926,402
Income (Loss) Before Income Taxes	831,208		797,457		1,089,366		827,236		1,088,340		1,446,363		892,936		813,359
Income Tax Provision (Benefit)	194,687		182,335		241,525		191,810		195,572		255,411		196,205		174,770		810,357	821,958	(1,921,397)
Net Income (Loss)	$ 636,521		$ 615,122		$ 847,841		$ 635,426		$ 892,768		$ 1,190,952		$ 696,731		$ 638,589		$ 2,734,910	$ 3,419,040	$ 2,582,579
Net Income (Loss) Per Share
Basic (in dollars per share)	$ 1.10	[1]	$ 1.06	[1]	$ 1.47	[1]	$ 1.10	[1]	$ 1.55	[1]	$ 2.06	[1]	$ 1.21	[1]	$ 1.11	[1]	$ 4.73	$ 5.93	$ 4.49
Diluted (in dollars per share)	$ 1.10	[1]	$ 1.06	[1]	$ 1.46	[1]	$ 1.10	[1]	$ 1.54	[1]	$ 2.05	[1]	$ 1.20	[1]	$ 1.10	[1]	$ 4.71	$ 5.89	$ 4.46
Average Number of Common Shares [Abstract]
Basic (in shares)	578,219		577,839		577,460		577,207		577,035		577,254		576,135		575,775		577,670	576,578	574,620
Diluted (in shares)	580,849		581,271		580,247		580,222		580,288		581,559		580,375		579,726		580,777	580,441	578,693

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