Loans and Allowance for Credit Losses, Loans by Portfolio Type (Details) - USD ($) $ in Thousands		Mar. 31, 2019	Dec. 31, 2018
Loan receivables disclosure [Abstract]
Loans, fixed rate of interest		$ 6,279,421	$ 5,749,373
Loans, variable rate of interest		15,326,982	15,744,110
Loans, non-accrual		152,577	163,247
Total		21,758,980	21,656,730
Accruing loans past due (90 days)	[1]	610	1,338
Credit Commitments [Abstract]
Outstanding commitments to extend credit		12,000,000
Commercial [Member]
Loan receivables disclosure [Abstract]
Loans, fixed rate of interest		3,336,747	2,251,188
Loans, variable rate of interest		10,534,870	11,285,049
Loans, non-accrual		90,358	99,841
Total		13,961,975	13,636,078
Credit Commitments [Abstract]
Outstanding standby letters of credit		720,000
Commercial real estate [Member]
Loan receivables disclosure [Abstract]
Loans, fixed rate of interest		1,004,692	1,477,274
Loans, variable rate of interest		3,574,451	3,265,918
Loans, non-accrual		21,508	21,621
Total		4,600,651	4,764,813
Residential mortgage [Member]
Loan receivables disclosure [Abstract]
Loans, fixed rate of interest		1,777,510	1,830,224
Loans, variable rate of interest		374,701	358,254
Loans, non-accrual		40,409	41,555
Total		2,192,620	2,230,033
Personal [Member]
Loan receivables disclosure [Abstract]
Loans, fixed rate of interest		160,472	190,687
Loans, variable rate of interest		842,960	834,889
Loans, non-accrual		302	230
Total		$ 1,003,734	$ 1,025,806

[1] Excludes residential mortgage loans guaranteed by agencies of the U.S. government