Parent Company Financial Statements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Assets
Overnight investments	$ 9,114,660	$ 4,347,336
Investment in marketable equity securities	97,528	91,680
Investment securities available for sale	9,203,427	7,014,243
Total other assets	1,657,356	783,953
Total assets	58,308,140	49,957,680
Liabilities and Shareholders' Equity
Long-term obligations	1,194,378	1,248,163
Other liabilities	381,326	391,552
Stockholders' equity	4,737,241	4,229,268	$ 3,586,184	$ 3,488,954
Total liabilities and shareholders' equity	58,308,140	49,957,680
Income Statement [Abstract]
Interest expense	60,676	95,857	92,642
Net interest income	1,390,334	1,388,169	1,311,369
Dividends from subsidiaries	173,091	229,700	149,800
Income tax benefit	154,202	126,159	134,677
Net income	547,459	491,723	457,371
Net income available to common shareholders	528,915	477,661	457,371
OPERATING ACTIVITIES
Net income	547,459	491,723	457,371
Net amortization of premiums and accretion of discounts	11,151	(8,513)	(27,263)
Marketable equity securities gains, net	(34,081)	(29,395)	(20,625)
Change in other assets	(12,910)	(7,286)	(24,274)
Change in other liabilities	6,854	(6,115)	(15,992)
Net cash provided by (Used in) Operating Activities	(283,783)	375,819	578,248
INVESTING ACTIVITIES
Net change in overnight investments	(4,767,324)	(3,204,363)	(65,181)
Purchases of marketable equity securities	(1,563)	(333,140)	(26,166)
Proceeds from sales of marketable equity securities	29,796	352,835	56,749
Investments in Majority-owned Subsidiaries	0	(422,500)	0
Net Cash Provided by (Used in) Investing Activities	(7,568,426)	(9,907,562)	(1,596,148)
FINANCING ACTIVITIES
Net change in short-term borrowings	(52,386)	(96,746)	(27,703)
Proceeds from Issuance of Long-term Debt	0	(400,000)	(200,000)
Repurchase of common stock	0	(333,755)	(453,123)
Cash dividends paid	(41,612)	(30,393)	(18,137)
Net cash used by financing activities	7,827,975	9,517,072	1,067,179
Cash and due from banks at beginning of period	4,270,000
Cash and due from banks at end of period	9,030,000	4,270,000
Cash payments for
Income taxes	870,467	116,583	83,038
Net proceeds from subordinated notes issuance	0	345,849	0
Net proceeds from preferred stock issuance	0	339,937	0
Parent
Assets
Cash	173,719	49,716
Overnight investments	5,716	1,607
Investment in marketable equity securities	97,528	91,680
Investment securities available for sale	0	2,010
Investment in Banking Subsidiaries	4,987,350	4,621,676
Investment in Other Subsidiaries	3,237	3,241
Due from subsidiaries	0	786
Total other assets	41,874	48,591
Total assets	5,309,424	4,819,307
Liabilities and Shareholders' Equity
Short-term borrowings	453,313	452,350
Long-term obligations	107,825	128,125
Due to Affiliate	2,829	0
Other liabilities	8,216	9,564
Stockholders' equity	4,737,241	4,229,268
Total liabilities and shareholders' equity	5,309,424	4,819,307
Income Statement [Abstract]
Interest income	2,011	3,952	1,327
Interest expense	16,578	16,817	7,187
Net interest income	(14,567)	(12,865)	(5,860)
Dividends from subsidiaries		229,685
Dividend Income, Banking Subsidiaries			149,819
Marketable equity securities losses, net	34,081	29,395	20,625
Other income (loss)	66	574	257
Other operating expense	11,275	13,168	9,497
Income before income tax benefit and equity in undistributed net income of subsidiaries	181,396	233,621	155,344
Income tax benefit	2,089	879	892
Income before equity in undistributed net income of subsidiaries	179,307	232,742	154,452
Excess distributions (undistributed ) net income of subsidiaries	(368,152)	(258,981)	(302,919)
Net income	547,459	491,723	457,371
Preferred stock dividends	18,544	14,062	0
Net income available to common shareholders	528,915	477,661	457,371
OPERATING ACTIVITIES
Net income	547,459	491,723	457,371
Excess distributions (undistributed ) net income of subsidiaries	(368,152)	(258,981)	(302,919)
Net amortization of premiums and accretion of discounts	963	824	119
Gain (Loss) on Disposition of Other Assets	(3,615)	2,456	2,185
Change in other assets	6,722	(3,074)	(2,001)
Securities (gains) losses	0	0	(20)
Change in other liabilities	3,265	(694)	981
Net cash provided by (Used in) Operating Activities	159,791	197,947	130,721
INVESTING ACTIVITIES
Net change in loans	0	0	100,000
Net change in overnight investments	(4,109)	940	2,162
Purchases of marketable equity securities	(1,563)	(333,140)	(26,166)
Proceeds from sales of marketable equity securities	29,796	352,835	56,749
Maturities and sales of investment securities	2,000	1,000	3,477
Net Cash Provided by (Used in) Investing Activities	26,124	(400,865)	136,222
FINANCING ACTIVITIES
Net change in short-term borrowings	0	(40,277)	40,277
Repayment of long-term obligations	(20,300)	(33,300)	(3,575)
Proceeds from Issuance of Long-term Debt	0	0	165,000
Repurchase of common stock	0	(333,755)	(453,123)
Cash dividends paid	(41,612)	(30,393)	(18,137)
Net cash used by financing activities	(61,912)	248,061	(269,558)
Net change in cash	124,003	45,143	(2,615)
Cash and due from banks at beginning of period	49,716	4,573	7,188
Cash and due from banks at end of period	173,719	49,716	4,573
Cash payments for
Interest	16,579	13,338	7,187
Income taxes	810,116	106,618	78,345
Net proceeds from subordinated notes issuance	0	345,849	0
Net proceeds from preferred stock issuance	$ 0	$ 339,937	$ 0