Securities - Scheduled Contractual Maturities of AFS (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Amortized cost
Within One Year	$ 585,081
After One Year through Five Years	889,723
After Five Years through Ten Years	958,273
After Ten Years	12,112,961
Total	14,546,038	$ 13,619,781
Fair value
Within One Year	577,212
After One Year through Five Years	873,863
After Five Years through Ten Years	833,293
After Ten Years	11,809,115
Total	$ 14,093,483
Weighted-average yield
Within One Year	1.37%
After One Year through Five Years	3.06%
After Five Years through Ten Years	2.58%
After Ten Years	4.54%
Total	4.19%
U.S. Treasury securities
Amortized cost
Within One Year	$ 490,798
After One Year through Five Years	597,938
After Five Years through Ten Years	167,614
After Ten Years	0
Total	1,256,350	1,010,053
Fair value
Within One Year	482,999
After One Year through Five Years	589,040
After Five Years through Ten Years	165,748
After Ten Years	0
Total	$ 1,237,787
Weighted-average yield
Within One Year	1.13%
After One Year through Five Years	3.22%
After Five Years through Ten Years	3.79%
After Ten Years	0.00%
Total	2.48%
U.S. government agency and U.S. government-sponsored enterprise debt securities
Amortized cost
Within One Year	$ 1,677
After One Year through Five Years	50,000
After Five Years through Ten Years	178,331
After Ten Years	57,495
Total	287,503	287,687
Fair value
Within One Year	1,656
After One Year through Five Years	47,873
After Five Years through Ten Years	157,707
After Ten Years	48,627
Total	$ 255,863
Weighted-average yield
Within One Year	2.85%
After One Year through Five Years	2.00%
After Five Years through Ten Years	2.08%
After Ten Years	2.16%
Total	2.09%
U.S. government agency and U.S. government-sponsored enterprise mortgage-backed securities
Amortized cost
Within One Year	$ 0
After One Year through Five Years	48,534
After Five Years through Ten Years	90,730
After Ten Years	11,143,055
Total	11,282,319
Fair value
Within One Year	0
After One Year through Five Years	46,851
After Five Years through Ten Years	83,689
After Ten Years	10,964,559
Total	$ 11,095,099
Weighted-average yield
Within One Year	0.00%
After One Year through Five Years	2.86%
After Five Years through Ten Years	2.90%
After Ten Years	4.74%
Total	4.71%
Municipal securities
Amortized cost
Within One Year	$ 7,800
After One Year through Five Years	17,636
After Five Years through Ten Years	22,598
After Ten Years	227,314
Total	275,348	277,275
Fair value
Within One Year	7,720
After One Year through Five Years	17,155
After Five Years through Ten Years	19,344
After Ten Years	193,740
Total	$ 237,959
Weighted-average yield
Within One Year	1.21%
After One Year through Five Years	2.58%
After Five Years through Ten Years	2.40%
After Ten Years	2.26%
Total	2.26%
Non-agency mortgage-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	629,132
Total	629,132
Fair value
Within One Year	0
After One Year through Five Years	0
After Five Years through Ten Years	0
After Ten Years	548,367
Total	$ 548,367
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	2.24%
Total	2.24%
Corporate debt securities
Amortized cost
Within One Year	$ 15,158
After One Year through Five Years	46,000
After Five Years through Ten Years	449,000
After Ten Years	25,000
Total	535,158	554,158
Fair value
Within One Year	15,058
After One Year through Five Years	42,999
After Five Years through Ten Years	366,134
After Ten Years	23,392
Total	$ 447,583
Weighted-average yield
Within One Year	4.70%
After One Year through Five Years	4.31%
After Five Years through Ten Years	2.36%
After Ten Years	1.80%
Total	2.57%
Foreign government bonds
Amortized cost
Within One Year	$ 69,648
After One Year through Five Years	129,615
After Five Years through Ten Years	50,000
After Ten Years	0
Total	249,263	247,249
Fair value
Within One Year	69,779
After One Year through Five Years	129,945
After Five Years through Ten Years	40,671
After Ten Years	0
Total	$ 240,395
Weighted-average yield
Within One Year	2.29%
After One Year through Five Years	2.46%
After Five Years through Ten Years	1.75%
After Ten Years	0.00%
Total	2.27%
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	30,965
Total	30,965	$ 31,886
Fair value
Within One Year	0
After One Year through Five Years	0
After Five Years through Ten Years	0
After Ten Years	30,430
Total	$ 30,430
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	4.36%
Total	4.36%