Consolidated Statement of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	ASU 2016-13 [Member]	Series A And Series C [Member]	Series G Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member] Series A And Series C [Member]	Preferred Stock [Member] Series G Preferred Stock [Member]	Common Stock [Member]	Common Stock Issuable [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] Series G Preferred Stock [Member]	Additional Paid-in Capital [Member] Series A Warrants [Member]	Retained Earnings [Member]	Retained Earnings [Member] ASU 2016-13 [Member]	Accumulated Other Comprehensive Income (Loss), Net [Member]	Treasury Stock [Member]	Treasury Stock [Member] Series A Warrants [Member]
Beginning balance at Dec. 31, 2017	$ 16,250,819				$ 1,231,500			$ 79,909	$ 1,847	$ 6,590,855			$ 10,164,804		$ (363,814)	$ (1,454,282)
Cumulative effect of change in accounting principle — equity securities	(16,853)												16,853		(16,853)
Total comprehensive income	1,878,666												1,918,080		(39,414)
Preferred stock cash dividends	(72,521)												(72,521)
Exercise of 257,630 Series A stock warrants into 136,676 shares of common stock												$ (22,394)					$ 22,394
Purchases of treasury stock	(2,194,396)															(2,194,396)
Stock-based compensation transactions, net	108,081							(26)	(121)	10,881			(86)			97,433
Common stock cash dividends	(510,458)												(510,458)
Ending balance at Dec. 31, 2018	15,460,191				1,231,500			79,883	1,726	6,579,342			11,516,672		(420,081)	(3,528,851)
Total comprehensive income	2,142,550												1,929,149		213,401
Preferred stock cash dividends	(72,482)												(72,482)
Redemption of Series A and Series C preferred stock			$ (381,500)			$ (381,500)
Issuance of Series G preferred stock				$ 396,000			$ 400,000				$ (4,000)
Purchases of treasury stock	(1,349,785)															(1,349,785)
Stock-based compensation transactions, net	73,891							(12)	(160)	18,197			(207)			56,073
Common stock cash dividends	(552,216)												(552,216)
Ending 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)
Cumulative effect of change inaccounting principle — credit losses		$ (91,925)												$ (91,925)
Total comprehensive income	1,496,800												1,353,152		143,648
Preferred stock cash dividends	(68,228)												(68,228)
Purchases of treasury stock	(373,750)															(373,750)
Stock-based compensation transactions, net	76,813								(222)	23,865			(411)			53,581
Common stock cash dividends	(569,076)												(569,076)
Ending 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)