Securities (Scheduled Contractual Maturities of AFS) (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Amortized cost
Within One Year	$ 126,627
After One Year through Five Years	913,928
After Five Years through Ten Years	860,523
After Ten Years	5,190,503
Amortized Cost	7,091,581	$ 10,087,179
Fair value
Within One Year	126,506
After One Year through Five Years	879,400
After Five Years through Ten Years	826,963
After Ten Years	4,896,562
Total	$ 6,729,431	9,965,353
Weighted Average Yield
Within One Year	1.99%
After One Year through Five Years	1.89%
After Five Years through Ten Years	2.39%
After Ten Years	1.83%
Total	1.91%
U.S. Treasury securities
Amortized cost
Within One Year	$ 0
After One Year through Five Years	576,650
After Five Years through Ten Years	99,680
After Ten Years	0
Amortized Cost	676,330	1,049,238
Fair value
Within One Year	0
After One Year through Five Years	547,431
After Five Years through Ten Years	90,543
After Ten Years	0
Total	$ 637,974	1,032,681
Weighted Average Yield
Within One Year	0.00%
After One Year through Five Years	1.28%
After Five Years through Ten Years	0.74%
After Ten Years	0.00%
Total	1.20%
U.S. government-sponsored enterprises debt securities
Amortized cost
Within One Year	$ 0
After One Year through Five Years	29,199
After Five Years through Ten Years	125,000
After Ten Years	172,356
Amortized Cost	326,555	1,333,984
Fair value
Within One Year	0
After One Year through Five Years	27,969
After Five Years through Ten Years	115,734
After Ten Years	160,692
Total	$ 304,395	1,301,971
Weighted Average Yield
Within One Year	0.00%
After One Year through Five Years	1.64%
After Five Years through Ten Years	1.16%
After Ten Years	2.09%
Total	1.70%
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	12,508
After Five Years through Ten Years	190,547
After Ten Years	2,610,226
Amortized Cost	2,813,281
Fair value
Within One Year	0
After One Year through Five Years	12,538
After Five Years through Ten Years	185,605
After Ten Years	2,470,665
Total	$ 2,668,808
Weighted Average Yield
Within One Year	0.00%
After One Year through Five Years	3.08%
After Five Years through Ten Years	2.62%
After Ten Years	1.78%
Total	1.85%
Municipal securities
Amortized cost
Within One Year	$ 1,841
After One Year through Five Years	36,444
After Five Years through Ten Years	18,691
After Ten Years	260,976
Amortized Cost	317,952	519,381
Fair value
Within One Year	1,844
After One Year through Five Years	35,640
After Five Years through Ten Years	18,174
After Ten Years	243,001
Total	$ 298,659	523,158
Weighted Average Yield
Within One Year	2.72%
After One Year through Five Years	2.41%
After Five Years through Ten Years	2.60%
After Ten Years	2.23%
Total	2.28%
Non-agency mortgage-backed securities
Amortized cost
Within One Year	$ 10,807
After One Year through Five Years	202,260
After Five Years through Ten Years	45,103
After Ten Years	1,065,535
Amortized Cost	1,323,705
Fair value
Within One Year	10,798
After One Year through Five Years	198,659
After Five Years through Ten Years	44,661
After Ten Years	997,989
Total	$ 1,252,107
Weighted Average Yield
Within One Year	3.07%
After One Year through Five Years	3.25%
After Five Years through Ten Years	1.16%
After Ten Years	2.00%
Total	2.17%
Corporate debt securities
Amortized cost
Within One Year	$ 0
After One Year through Five Years	10,000
After Five Years through Ten Years	331,502
After Ten Years	342,000
Amortized Cost	683,502	657,516
Fair value
Within One Year	0
After One Year through Five Years	9,848
After Five Years through Ten Years	322,115
After Ten Years	298,549
Total	$ 630,512	649,665
Weighted Average Yield
Within One Year	0.00%
After One Year through Five Years	1.55%
After Five Years through Ten Years	3.67%
After Ten Years	2.05%
Total	2.83%
Foreign government bonds
Amortized cost
Within One Year	$ 113,979
After One Year through Five Years	46,867
After Five Years through Ten Years	50,000
After Ten Years	50,000
Amortized Cost	260,846	260,447
Fair value
Within One Year	113,864
After One Year through Five Years	47,315
After Five Years through Ten Years	50,131
After Ten Years	42,501
Total	$ 253,811	257,733
Weighted Average Yield
Within One Year	1.88%
After One Year through Five Years	3.01%
After Five Years through Ten Years	0.42%
After Ten Years	1.50%
Total	1.73%
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	72,160
Amortized Cost	72,160	74,674
Fair value
Within One Year	0
After One Year through Five Years	0
After Five Years through Ten Years	0
After Ten Years	71,362
Total	$ 71,362	74,558
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	1.50%
Total	1.50%
Collateralized loan obligations (“CLOs”)
Amortized cost
Within One Year	$ 0
After One Year through Five Years	0
After Five Years through Ten Years	0
After Ten Years	617,250
Amortized Cost	617,250	592,250
Fair value
Within One Year	0
After One Year through Five Years	0
After Five Years through Ten Years	0
After Ten Years	611,803
Total	$ 611,803	$ 589,950
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	1.41%
Total	1.41%