Consolidated Statement of Changes in Shareholders' Equity - USD ($) $ in Thousands		Total	ASU 2016-13 [Member]	Preferred Stock [Member]	Common Stock [Member]	Common Stock Issuable [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Retained Earnings [Member] ASU 2016-13 [Member]	Accumulated Other Comprehensive Income (Loss), Net [Member]	Treasury Stock [Member]
Beginning balance at Dec. 31, 2019		$ 15,716,649		$ 1,250,000	$ 79,871	$ 1,566	$ 6,593,539	$ 12,820,916		$ (206,680)	$ (4,822,563)
Adoption of new accounting standard for credit losses			$ (91,925)						$ (91,925)
Total comprehensive income		685,335						268,822		416,513
Preferred stock cash dividends	[1]	(17,078)						(17,078)
Purchases of treasury stock		(373,750)									(373,750)
Stock-based compensation transactions, net		39,806				(274)	(5,132)	(102)			45,314
Common stock cash dividends		(143,243)						(143,243)
Ending balance at Mar. 31, 2020		15,815,794		1,250,000	79,871	1,292	6,588,407	12,837,390		209,833	(5,150,999)
Beginning balance at Dec. 31, 2020		16,187,283		1,250,000	79,871	1,344	6,617,404	13,444,428		(63,032)	(5,142,732)
Total comprehensive income		371,803						447,249		(75,446)
Preferred stock cash dividends	[1]	(17,050)						(17,050)
Stock-based compensation transactions, net		46,998				(179)	(6,254)	(208)			53,639
Common stock cash dividends		(142,526)						(142,526)
Ending balance at Mar. 31, 2021		$ 16,446,508		$ 1,250,000	$ 79,871	$ 1,165	$ 6,611,150	$ 13,731,893		$ (138,478)	$ (5,089,093)

[1] For the three-months ended March 31, 2021, dividends per preferred share were: Preferred Series E - $16.125; Preferred Series F - $128.125; and Preferred Series G - $125.00.  Dividends per preferred share for the three-months ended March 31, 2020 were:  Preferred Series E - $16.125; Preferred Series F - $128.125; and Preferred Series G - $125.694.