Loans, Loans by Past Due Status (Details) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Summarized details of Loans
Current		$ 22,679,696	$ 22,785,019
Financing Receivable, Recorded Investment, Nonaccrual Status		118,380	127,901
Loans and Leases Receivable, Net of Deferred Income		22,821,440	22,940,429
Nonaccrual Loans, Current Portion		$ 48,000	$ 74,000
Percent of current nonaccrual loans		41.00%	58.00%
Pass
Summarized details of Loans
Loans and Leases Receivable, Net of Deferred Income		$ 22,294,939	$ 22,438,605
Nonaccrual
Summarized details of Loans
Loans and Leases Receivable, Net of Deferred Income		118,380	127,901
30-59 Days Past Due
Summarized details of Loans
Total Past Due		18,188	21,550
60-89 Days Past Due
Summarized details of Loans
Total Past Due		2,916	3,795
90 Days or More Past Due
Summarized details of Loans
Total Past Due		2,259	2,165
30-89 Days Past Due
Summarized details of Loans
Approximate Carrying Amount of Loans Sold	approximately $200,000
Commercial and industrial
Summarized details of Loans
Current		7,307,118	7,356,187
Financing Receivable, Recorded Investment, Nonaccrual Status		46,312	41,021
Loans and Leases Receivable, Net of Deferred Income		7,354,594	7,398,044
Commercial and industrial | Pass
Summarized details of Loans
Loans and Leases Receivable, Net of Deferred Income		7,118,448	7,162,370
Commercial and industrial | Nonaccrual
Summarized details of Loans
Loans and Leases Receivable, Net of Deferred Income		46,312	41,021
Commercial and industrial | 30-59 Days Past Due
Summarized details of Loans
Total Past Due		576	187
Commercial and industrial | 60-89 Days Past Due
Summarized details of Loans
Total Past Due		245	338
Commercial and industrial | 90 Days or More Past Due
Summarized details of Loans
Total Past Due		342	311
Commercial real estate - owner occupied
Summarized details of Loans
Current		909,828	913,787
Financing Receivable, Recorded Investment, Nonaccrual Status		67	3,957
Loans and Leases Receivable, Net of Deferred Income		911,265	920,443
Commercial real estate - owner occupied | Pass
Summarized details of Loans
Loans and Leases Receivable, Net of Deferred Income		866,193	854,265
Commercial real estate - owner occupied | Nonaccrual
Summarized details of Loans
Loans and Leases Receivable, Net of Deferred Income		67	3,957
Commercial real estate - owner occupied | 30-59 Days Past Due
Summarized details of Loans
Total Past Due		1,369	2,580
Commercial real estate - owner occupied | 60-89 Days Past Due
Summarized details of Loans
Total Past Due		0	119
Commercial real estate - owner occupied | 90 Days or More Past Due
Summarized details of Loans
Total Past Due		0	0
Commercial and business lending
Summarized details of Loans
Current		8,216,947	8,269,974
Financing Receivable, Recorded Investment, Nonaccrual Status		46,380	44,978
Loans and Leases Receivable, Net of Deferred Income		8,265,858	8,318,487
Commercial and business lending | Pass
Summarized details of Loans
Loans and Leases Receivable, Net of Deferred Income		7,984,641	8,016,635
Commercial and business lending | Nonaccrual
Summarized details of Loans
Loans and Leases Receivable, Net of Deferred Income		46,380	44,978
Commercial and business lending | 30-59 Days Past Due
Summarized details of Loans
Total Past Due		1,945	2,767
Commercial and business lending | 60-89 Days Past Due
Summarized details of Loans
Total Past Due		245	457
Commercial and business lending | 90 Days or More Past Due
Summarized details of Loans
Total Past Due		342	311
Commercial real estate - investor
Summarized details of Loans
Current		3,788,296	3,745,835
Financing Receivable, Recorded Investment, Nonaccrual Status		4,409	1,952
Loans and Leases Receivable, Net of Deferred Income		3,794,517	3,751,554
Commercial real estate - investor | Pass
Summarized details of Loans
Loans and Leases Receivable, Net of Deferred Income		3,620,785	3,653,642
Commercial real estate - investor | Nonaccrual
Summarized details of Loans
Loans and Leases Receivable, Net of Deferred Income		4,409	1,952
Commercial real estate - investor | 30-59 Days Past Due
Summarized details of Loans
Total Past Due		1,812	2,954
Commercial real estate - investor | 60-89 Days Past Due
Summarized details of Loans
Total Past Due		0	813
Commercial real estate - investor | 90 Days or More Past Due
Summarized details of Loans
Total Past Due		0	0
Real estate construction
Summarized details of Loans
Current		1,420,310	1,333,722
Financing Receivable, Recorded Investment, Nonaccrual Status		493	979
Loans and Leases Receivable, Net of Deferred Income		1,420,900	1,335,031
Real estate construction | Pass
Summarized details of Loans
Loans and Leases Receivable, Net of Deferred Income		1,420,374	1,321,447
Real estate construction | Nonaccrual
Summarized details of Loans
Loans and Leases Receivable, Net of Deferred Income		493	979
Real estate construction | 30-59 Days Past Due
Summarized details of Loans
Total Past Due		64	330
Real estate construction | 60-89 Days Past Due
Summarized details of Loans
Total Past Due		33	0
Real estate construction | 90 Days or More Past Due
Summarized details of Loans
Total Past Due		0	0
Commercial real estate lending
Summarized details of Loans
Current		5,208,606	5,079,557
Financing Receivable, Recorded Investment, Nonaccrual Status		4,902	2,931
Loans and Leases Receivable, Net of Deferred Income		5,215,417	5,086,585
Commercial real estate lending | 30-59 Days Past Due
Summarized details of Loans
Total Past Due		1,876	3,284
Commercial real estate lending | 60-89 Days Past Due
Summarized details of Loans
Total Past Due		33	813
Commercial real estate lending | 90 Days or More Past Due
Summarized details of Loans
Total Past Due		0	0
Total commercial
Summarized details of Loans
Current		13,425,552	13,349,531
Financing Receivable, Recorded Investment, Nonaccrual Status		51,282	47,909
Loans and Leases Receivable, Net of Deferred Income		13,481,275	13,405,072
Total commercial | 30-59 Days Past Due
Summarized details of Loans
Total Past Due		3,821	6,051
Total commercial | 60-89 Days Past Due
Summarized details of Loans
Total Past Due		278	1,270
Total commercial | 90 Days or More Past Due
Summarized details of Loans
Total Past Due		342	311
Residential mortgage
Summarized details of Loans
Current		8,069,863	8,200,432
Financing Receivable, Recorded Investment, Nonaccrual Status		57,844	67,574
Loans and Leases Receivable, Net of Deferred Income		8,136,980	8,277,712
Approximate Carrying Amount of Loans Sold	approximately $240 million
Residential mortgage | Pass
Summarized details of Loans
Loans and Leases Receivable, Net of Deferred Income		8,077,122	8,203,729
Residential mortgage | Nonaccrual
Summarized details of Loans
Loans and Leases Receivable, Net of Deferred Income		57,844	67,574
Residential mortgage | 30-59 Days Past Due
Summarized details of Loans
Total Past Due		8,749	9,272
Residential mortgage | 60-89 Days Past Due
Summarized details of Loans
Total Past Due		525	434
Residential mortgage | 90 Days or More Past Due
Summarized details of Loans
Total Past Due		0	0
Home equity
Summarized details of Loans
Current		837,274	876,085
Financing Receivable, Recorded Investment, Nonaccrual Status		9,104	12,339
Loans and Leases Receivable, Net of Deferred Income		852,025	894,473
Home equity | Pass
Summarized details of Loans
Loans and Leases Receivable, Net of Deferred Income		841,757	880,808
Home equity | Nonaccrual
Summarized details of Loans
Loans and Leases Receivable, Net of Deferred Income		9,104	12,339
Home equity | 30-59 Days Past Due
Summarized details of Loans
Total Past Due		4,483	4,826
Home equity | 60-89 Days Past Due
Summarized details of Loans
Total Past Due		1,164	1,223
Home equity | 90 Days or More Past Due
Summarized details of Loans
Total Past Due		0	0
Other consumer
Summarized details of Loans
Current		347,007	358,970
Financing Receivable, Recorded Investment, Nonaccrual Status		152	79
Loans and Leases Receivable, Net of Deferred Income		351,159	363,171
Other consumer | Pass
Summarized details of Loans
Loans and Leases Receivable, Net of Deferred Income		350,260	362,343
Other consumer | Nonaccrual
Summarized details of Loans
Loans and Leases Receivable, Net of Deferred Income		152	79
Other consumer | 30-59 Days Past Due
Summarized details of Loans
Total Past Due		1,135	1,401
Other consumer | 60-89 Days Past Due
Summarized details of Loans
Total Past Due		949	868
Other consumer | 90 Days or More Past Due
Summarized details of Loans
Total Past Due		1,917	1,853
Total consumer
Summarized details of Loans
Current		9,254,144	9,435,487
Financing Receivable, Recorded Investment, Nonaccrual Status		67,099	79,992
Loans and Leases Receivable, Net of Deferred Income		9,340,164	9,535,357
Total consumer | 30-59 Days Past Due
Summarized details of Loans
Total Past Due		14,366	15,499
Total consumer | 60-89 Days Past Due
Summarized details of Loans
Total Past Due		2,638	2,525
Total consumer | 90 Days or More Past Due
Summarized details of Loans
Total Past Due		1,917	1,853
Total consumer
Summarized details of Loans
Loans and Leases Receivable, Net of Deferred Income		9,340,164	9,535,357
Carrying Amount Of Loans Sold	$ 33,000
Total consumer | Pass
Summarized details of Loans
Loans and Leases Receivable, Net of Deferred Income		9,269,139	9,446,881
Carrying Amount Of Loans Sold	21,000
Total consumer | Nonaccrual
Summarized details of Loans
Loans and Leases Receivable, Net of Deferred Income		$ 67,099	$ 79,992
Carrying Amount Of Loans Sold	$ 12,000