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		961,186						509,876		451,310
Preferred stock cash dividends	[1]	(34,128)						(34,128)
Purchases of treasury stock		(373,750)									(373,750)
Stock-based compensation transactions, net		52,261				(258)	5,530	(206)			47,195
Common stock cash dividends		(285,188)						(285,188)
Ending balance at Jun. 30, 2020		15,945,105		1,250,000	79,871	1,308	6,599,069	12,919,345		244,630	(5,149,118)
Beginning 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)
Total comprehensive income		275,851						241,054		34,797
Preferred stock cash dividends	[1]	(17,050)						(17,050)
Stock-based compensation transactions, net		12,455				16	10,662	(104)			1,881
Common stock cash dividends		(141,945)						(141,945)
Ending balance at Jun. 30, 2020		15,945,105		1,250,000	79,871	1,308	6,599,069	12,919,345		244,630	(5,149,118)
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		791,376						905,318		(113,942)
Preferred stock cash dividends	[1]	(34,100)						(34,100)
Stock-based compensation transactions, net		60,767				(165)	3,124	(409)			58,217
Common stock cash dividends		(285,022)						(285,022)
Ending balance at Jun. 30, 2021		16,720,304		1,250,000	79,871	1,179	6,620,528	14,030,215		(176,974)	(5,084,515)
Beginning 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)
Total comprehensive income		419,573						458,069		(38,496)
Preferred stock cash dividends	[1]	(17,050)						(17,050)
Stock-based compensation transactions, net		13,769				14	9,378	(201)			4,578
Common stock cash dividends		(142,496)						(142,496)
Ending balance at Jun. 30, 2021		$ 16,720,304		$ 1,250,000	$ 79,871	$ 1,179	$ 6,620,528	$ 14,030,215		$ (176,974)	$ (5,084,515)

[1] For the three-month and six-month periods ended June 30, 2021, dividends per preferred share were: Preferred Series E - $16.125 and $32.25, respectively; Preferred Series F - $128.125 and $256.25, respectively; and Preferred Series G - $125.00 and $250.00, respectively.  Dividends per preferred share for the three-month and six-month periods ended June 30, 2020 were:  Preferred Series E - $16.125 and $32.25, respectively; Preferred Series F - $128.125 and $256.25, respectively; and Preferred Series G - $125.00 and $250.694, respectively.