Consolidated Statement of Income (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Interest income
Loans and leases, including fees	$ 1,024,471	$ 924,640	$ 2,004,440	$ 1,822,678
Investment securities
Fully taxable	82,019	92,996	164,871	188,120
Exempt from federal taxes	172	379	420	809
Deposits at banks	21,869	12,213	40,546	24,375
Other	374	185	778	464
Total interest income	1,128,905	1,030,413	2,211,055	2,036,446
Interest expense
Savings and interest-checking deposits	48,738	30,543	89,265	56,177
Time deposits	11,362	16,303	22,298	35,301
Deposits at Cayman Islands office	542	281	923	546
Short-term borrowings	1,383	378	2,266	594
Long-term borrowings	58,093	44,708	111,999	91,368
Total interest expense	120,118	92,213	226,751	183,986
Net interest income	1,008,787	938,200	1,984,304	1,852,460
Provision for credit losses	35,000	52,000	78,000	107,000
Net interest income after provision for credit losses	973,787	886,200	1,906,304	1,745,460
Other income
Brokerage services income	12,629	16,617	26,021	34,001
Trading account and foreign exchange gains	5,255	8,084	9,892	17,775
Gain (loss) on bank investment securities	2,326	(17)	(7,105)	(17)
Other revenues from operations	100,280	117,115	226,582	228,002
Total other income	457,414	460,816	916,110	907,661
Other expense
Salaries and employee benefits	418,537	398,054	881,965	847,795
Equipment and net occupancy	73,031	73,797	147,828	148,163
Outside data processing and software	49,712	44,575	98,141	88,876
FDIC assessments	19,560	25,353	39,840	54,180
Advertising and marketing	21,768	16,324	38,016	32,434
Printing, postage and supplies	8,719	8,957	18,038	18,665
Amortization of core deposit and other intangible assets	6,388	8,113	13,020	16,533
Other costs of operations	178,862	175,462	473,073	331,841
Total other expense	776,577	750,635	1,709,921	1,538,487
Income before taxes	654,624	596,381	1,112,493	1,114,634
Income taxes	161,464	215,328	266,723	384,654
Net income	493,160	381,053	845,770	729,980
Net income available to common shareholders
Basic	472,598	360,658	805,338	689,208
Diluted	$ 472,600	$ 360,662	$ 805,342	$ 689,217
Net income per common share
Basic	$ 3.26	$ 2.36	$ 5.49	$ 4.49
Diluted	3.26	2.35	5.48	4.47
Cash dividends per common share	$ 0.80	$ 0.75	$ 1.55	$ 1.50
Average common shares outstanding
Basic	144,825	152,857	146,746	153,638
Diluted	144,998	153,276	146,941	154,108
Mortgage Banking Revenues [Member]
Other income
Revenue from contract with customer	$ 92,499	$ 86,163	$ 179,805	$ 170,855
Service Charges on Deposit Accounts [Member]
Other income
Revenue from contract with customer	106,784	106,057	211,899	210,233
Trust Income [Member]
Other income
Revenue from contract with customer	$ 137,641	$ 126,797	$ 269,016	$ 246,812