Financial Derivatives - Schedule of Derivative Instruments in Statement of Financial Position (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Notional Disclosures [Abstract]
Notional Amount	$ 15,921,182	$ 15,447,553
Asset
Asset	15,668	17,468
Collateral (held)/pledged	(2,198)	(1,345)
Net amount	13,470	16,123
(Liability)
(Liability)	(25,633)	(29,892)
Collateral (held)/pledged	175,189	212,263
Financial derivatives	149,556	182,371
Designated as hedge | Fair value hedges: | Pay fixed non-callable
Notional Disclosures [Abstract]
Notional Amount	5,322,606	5,463,303
Asset
Asset	7,407	10,157
(Liability)
(Liability)	$ (770)	$ (2,585)
Weighted- Average Pay Rate	2.20%	2.26%
Weighted- Average Receive Rate	0.12%	0.21%
Weighted- Average Remaining Term (in years)	12 years 1 month 17 days	11 years 11 months 12 days
Designated as hedge | Fair value hedges: | Receive fixed non-callable
Notional Disclosures [Abstract]
Notional Amount	$ 4,748,529	$ 2,611,029
Asset
Asset	22	2
(Liability)
(Liability)	$ (9,657)	$ (8,755)
Weighted- Average Pay Rate	0.17%	0.32%
Weighted- Average Receive Rate	0.90%	1.61%
Weighted- Average Remaining Term (in years)	2 years 2 months 1 day	2 years 1 month 6 days
Designated as hedge | Fair value hedges: | Receive fixed callable
Notional Disclosures [Abstract]
Notional Amount	$ 1,459,577	$ 343,500
Asset
Asset	1,246	3,108
(Liability)
(Liability)	$ (5,108)	$ (4)
Weighted- Average Pay Rate	0.02%	0.16%
Weighted- Average Receive Rate	0.73%	1.78%
Weighted- Average Remaining Term (in years)	4 years 21 days	3 years 1 month 28 days
Designated as hedge | Cash flow hedges: | Pay fixed non-callable
Notional Disclosures [Abstract]
Notional Amount	$ 535,000	$ 472,000
Asset
Asset	6,121	2,584
(Liability)
(Liability)	$ (4,149)	$ (8,771)
Weighted- Average Pay Rate	1.96%	2.04%
Weighted- Average Receive Rate	0.49%	0.57%
Weighted- Average Remaining Term (in years)	5 years 8 months 8 days	6 years 14 days
No hedge designation
Asset
Credit valuation adjustment	$ (30)	$ (1)
(Liability)
Credit valuation adjustment	12	35
No hedge designation | Pay fixed non-callable
Notional Disclosures [Abstract]
Notional Amount	238,809	339,090
Asset
Asset	0	0
(Liability)
(Liability)	$ (5,826)	$ (9,675)
Weighted- Average Pay Rate	3.31%	2.38%
Weighted- Average Receive Rate	0.14%	0.19%
Weighted- Average Remaining Term (in years)	4 years 11 months 26 days	4 years 2 months 23 days
No hedge designation | Receive fixed non-callable
Notional Disclosures [Abstract]
Notional Amount	$ 1,373,250	$ 2,359,220
Asset
Asset	0	0
(Liability)
(Liability)	$ 0	$ 0
Weighted- Average Pay Rate	0.10%	0.16%
Weighted- Average Receive Rate	0.50%	0.87%
Weighted- Average Remaining Term (in years)	11 months 8 days	1 year 25 days
No hedge designation | Receive fixed callable
Notional Disclosures [Abstract]
Notional Amount		$ 200,000
Asset
Asset		1
(Liability)
(Liability)		$ (12)
Weighted- Average Pay Rate		0.13%
Weighted- Average Receive Rate		0.15%
Weighted- Average Remaining Term (in years)		8 months 19 days
No hedge designation | Basis swaps
Notional Disclosures [Abstract]
Notional Amount	$ 2,088,911	$ 3,628,911
Asset
Asset	902	1,617
(Liability)
(Liability)	$ (135)	$ (43)
Weighted- Average Pay Rate	0.14%	0.18%
Weighted- Average Receive Rate	0.18%	0.23%
Weighted- Average Remaining Term (in years)	2 years 9 months 7 days	2 years 10 days
No hedge designation | Treasury futures
Notional Disclosures [Abstract]
Notional Amount	$ 154,500	$ 30,500
Asset
Asset	0	0
(Liability)
(Liability)	$ 0	$ (82)
Weighted- Average Forward Price (in dollars per share)	$ 131.61	$ 137.81