Accumulated Other Comprehensive (Loss), Net of Tax - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Tax benefit	$ (64,777)	$ (47,941)	$ (121,514)	$ (117,287)
Interest payments	775,203	798,097	1,530,320	1,590,142
Premium amortization	1,000,587	976,286	1,974,074	1,928,136
Actuarial net loss amortization	(32,796)	(36,811)	(63,524)	(68,240)
Net income	258,848	181,633	485,765	397,956
Cash Flow Hedging
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Estimate of amount to be reclassified from AOCL	300		300
Investment Securities Available- for-Sale | Reclassification out of accumulated comprehensive income
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Net unrealized gains (losses)	0	(46,496)	528	(55,183)
Tax benefit	0	12,335	(143)	14,703
Net income	0	(34,161)	385	(40,480)
Derivative Financial Instruments | Reclassification out of accumulated comprehensive income
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Tax benefit	729	3,214	1,612	6,063
Interest payments	(2,689)	(11,630)	(5,944)	(22,122)
Hedge terminations	0	0	0	(34)
Premium amortization	0	(217)	0	(489)
Net income	(1,960)	(8,633)	(4,332)	(16,582)
Defined benefit pension and other postretirement benefit plans: | Reclassification out of accumulated comprehensive income
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Tax benefit	103	179	206	357
Net income	(277)	(479)	(554)	(958)
Actuarial net loss amortization | Reclassification out of accumulated comprehensive income
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Actuarial net loss amortization	$ (380)	$ (658)	$ (760)	$ (1,315)