Loans and Allowances for Credit Losses, Activity in Allowance for Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Allowance for loan losses [Roll Forward]
Beginning balance	$ 246,159	$ 225,524
Provision for loan losses	1,804	30,104
Loans charged off	(2,153)	(23,991)
Recoveries	2,900	1,519
Ending balance	248,710	233,156
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	11,244	1,711
Provision for off-balance sheet credit losses	(1,804)	4,896
Ending balance	9,440	6,607
Total provision for credit losses	0	35,000
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment			$ 16,784,290	$ 16,758,676	$ 15,780,736
Individually measured for impairment, recorded investment			207,616	230,984	241,830
Total			16,991,906	16,989,660	16,022,566
Related allowance [Abstract]
Collectively measured for impairment, related allowance			217,886	217,116	205,049
Individually measured for impairment, related allowance			3,497	843	2,686
Total	246,159	225,524	248,710	246,159	233,156
Commercial
Allowance for loan losses [Roll Forward]
Beginning balance	140,213	130,334
Provision for loan losses	(3,355)	31,097
Loans charged off	(424)	(22,126)
Recoveries	1,182	488
Ending balance	137,616	139,793
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	11,063	1,506
Provision for off-balance sheet credit losses	(1,775)	4,813
Ending balance	9,288	6,319
Total provision for credit losses	(5,130)	35,910
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment			10,170,285	10,211,871	10,113,773
Individually measured for impairment, recorded investment			156,825	178,953	174,652
Total			10,327,110	10,390,824	10,288,425
Related allowance [Abstract]
Collectively measured for impairment, related allowance			134,164	139,416	137,191
Individually measured for impairment, related allowance			3,452	797	2,602
Total	140,213	130,334	137,616	140,213	139,793
Commercial real estate
Allowance for loan losses [Roll Forward]
Beginning balance	50,749	41,391
Provision for loan losses	6,859	2,977
Loans charged off	0	0
Recoveries	735	85
Ending balance	58,343	44,453
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	123	153
Provision for off-balance sheet credit losses	(17)	75
Ending balance	106	228
Total provision for credit losses	6,842	3,052
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment			3,866,588	3,803,525	3,361,237
Individually measured for impairment, recorded investment			4,475	5,521	9,270
Total			3,871,063	3,809,046	3,370,507
Related allowance [Abstract]
Collectively measured for impairment, related allowance			58,343	50,749	44,435
Individually measured for impairment, related allowance			0	0	18
Total	50,749	41,391	58,343	50,749	44,453
Residential mortgage
Allowance for loan losses [Roll Forward]
Beginning balance	18,224	19,509
Provision for loan losses	(39)	(731)
Loans charged off	(236)	(474)
Recoveries	228	163
Ending balance	18,177	18,467
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	50	30
Provision for off-balance sheet credit losses	(10)	28
Ending balance	40	58
Total provision for credit losses	(49)	(703)
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment			1,900,193	1,903,612	1,811,732
Individually measured for impairment, recorded investment			46,081	46,220	57,577
Total			1,946,274	1,949,832	1,869,309
Related allowance [Abstract]
Collectively measured for impairment, related allowance			18,132	18,178	18,401
Individually measured for impairment, related allowance			45	46	66
Total	18,224	19,509	18,177	18,224	18,467
Personal
Allowance for loan losses [Roll Forward]
Beginning balance	8,773	4,164
Provision for loan losses	(788)	1,466
Loans charged off	(1,493)	(1,391)
Recoveries	755	783
Ending balance	7,247	5,022
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	8	22
Provision for off-balance sheet credit losses	(2)	(20)
Ending balance	6	2
Total provision for credit losses	(790)	1,446
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment			847,224	839,668	493,994
Individually measured for impairment, recorded investment			235	290	331
Total			847,459	839,958	494,325
Related allowance [Abstract]
Collectively measured for impairment, related allowance			7,247	8,773	5,022
Individually measured for impairment, related allowance			0	0	0
Total	8,773	4,164	7,247	8,773	5,022
Specific Allowance [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	217,959
Ending balance	221,383	207,735
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment			16,784,290	16,758,676	15,780,736
Individually measured for impairment, recorded investment			207,616	230,984	241,830
Total			16,991,906	16,989,660	16,022,566
Related allowance [Abstract]
Collectively measured for impairment, related allowance			217,886	217,116	205,049
Individually measured for impairment, related allowance			3,497	843	2,686
Total	217,959	207,735	221,383	217,959	207,735
Nonspecific Allowance [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	28,200	30,126
Provision for loan losses	(873)	(4,705)
Loans charged off	0	0
Recoveries	0	0
Ending balance	27,327	25,421
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	0	0
Provision for off-balance sheet credit losses	0	0
Ending balance	0	0
Total provision for credit losses	(873)	(4,705)
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment			0	0	0
Individually measured for impairment, recorded investment			0	0	0
Total			0	0	0
Related allowance [Abstract]
Collectively measured for impairment, related allowance			0	0	0
Individually measured for impairment, related allowance			0	0	0
Total	$ 28,200	$ 30,126	$ 27,327	$ 28,200	$ 25,421