Securities - Scheduled Contractual Maturities of AFS (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Dec. 31, 2024
Amortized cost
Within One Year	$ 511,271
After One Year through Five Years	653,228
After Five Years through Ten Years	818,657
After Ten Years	11,206,157
Total	13,189,313	$ 11,505,775
Fair value
Within One Year	507,629
After One Year through Five Years	633,745
After Five Years through Ten Years	729,367
After Ten Years	10,870,411
Total	$ 12,741,152
Weighted-average yield
Within One Year	2.73%
After One Year through Five Years	1.61%
After Five Years through Ten Years	2.77%
After Ten Years	4.79%
Total	4.42%
U.S. Treasury securities
Amortized cost
Within One Year	$ 339,871
After One Year through Five Years	486,357
After Five Years through Ten Years	49,349
After Ten Years	0
Total	875,577	676,300
Fair value
Within One Year	336,058
After One Year through Five Years	470,466
After Five Years through Ten Years	49,691
After Ten Years	0
Total	$ 856,215
Weighted-average yield
Within One Year	2.61%
After One Year through Five Years	1.32%
After Five Years through Ten Years	3.95%
After Ten Years	0.00%
Total	1.97%
U.S. government agency and U.S. government-sponsored enterprise debt securities
Amortized cost
Within One Year	$ 0
After One Year through Five Years	26,677
After Five Years through Ten Years	200,833
After Ten Years	60,858
Total	288,368	308,220
Fair value
Within One Year	0
After One Year through Five Years	26,066
After Five Years through Ten Years	178,519
After Ten Years	51,801
Total	$ 256,386
Weighted-average yield
Within One Year	0.00%
After One Year through Five Years	1.58%
After Five Years through Ten Years	2.06%
After Ten Years	2.19%
Total	2.05%
U.S. government agency and U.S. government-sponsored enterprise mortgage-backed securities
Amortized cost
Within One Year	$ 4,755
After One Year through Five Years	83,696
After Five Years through Ten Years	111,891
After Ten Years	9,975,959
Total	10,176,301
Fair value
Within One Year	4,741
After One Year through Five Years	81,229
After Five Years through Ten Years	103,361
After Ten Years	9,822,535
Total	$ 10,011,866
Weighted-average yield
Within One Year	3.57%
After One Year through Five Years	2.91%
After Five Years through Ten Years	2.94%
After Ten Years	5.10%
Total	5.05%
Municipal securities
Amortized cost
Within One Year	$ 9,098
After One Year through Five Years	21,298
After Five Years through Ten Years	22,629
After Ten Years	228,990
Total	282,015	287,301
Fair value
Within One Year	8,987
After One Year through Five Years	20,689
After Five Years through Ten Years	19,446
After Ten Years	196,060
Total	$ 245,182
Weighted-average yield
Within One Year	1.85%
After One Year through Five Years	2.41%
After Five Years through Ten Years	2.40%
After Ten Years	2.26%
Total	2.27%
Non-agency mortgage-backed securities
Amortized cost
Within One Year	$ 3,970
After One Year through Five Years	2,899
After Five Years through Ten Years	1,955
After Ten Years	682,701
Total	691,525
Fair value
Within One Year	3,924
After One Year through Five Years	2,875
After Five Years through Ten Years	1,955
After Ten Years	592,917
Total	$ 601,671
Weighted-average yield
Within One Year	5.21%
After One Year through Five Years	3.21%
After Five Years through Ten Years	5.34%
After Ten Years	2.28%
Total	2.30%
Corporate debt securities
Amortized cost
Within One Year	$ 35,900
After One Year through Five Years	4,000
After Five Years through Ten Years	382,000
After Ten Years	175,000
Total	596,900	653,500
Fair value
Within One Year	35,785
After One Year through Five Years	3,975
After Five Years through Ten Years	326,549
After Ten Years	134,561
Total	$ 500,870
Weighted-average yield
Within One Year	4.45%
After One Year through Five Years	4.00%
After Five Years through Ten Years	2.69%
After Ten Years	2.02%
Total	2.61%
Foreign government bonds
Amortized cost
Within One Year	$ 117,677
After One Year through Five Years	28,301
After Five Years through Ten Years	50,000
After Ten Years	50,000
Total	245,978	244,803
Fair value
Within One Year	118,134
After One Year through Five Years	28,445
After Five Years through Ten Years	49,846
After Ten Years	40,594
Total	$ 237,019
Weighted-average yield
Within One Year	2.49%
After One Year through Five Years	1.81%
After Five Years through Ten Years	4.74%
After Ten Years	1.50%
Total	2.67%
Asset-backed securities
Amortized cost
Within One Year	$ 0
After One Year through Five Years	0
After Five Years through Ten Years	0
After Ten Years	32,649
Total	32,649	$ 35,086
Fair value
Within One Year	0
After One Year through Five Years	0
After Five Years through Ten Years	0
After Ten Years	31,943
Total	$ 31,943
Weighted-average yield
Within One Year	0.00%
After One Year through Five Years	0.00%
After Five Years through Ten Years	0.00%
After Ten Years	5.04%
Total	5.04%