Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total other comprehensive income (loss)	$ (342,462)	$ (118,045)
Income tax benefit (expense)	71,917	24,789
Other comprehensive income (loss), net of tax	(270,545)	(93,256)
Amounts Reclassified From Accumulated Other Comprehensive Income [Abstract]
Total reclassifications before tax	219,439	189,617
Income tax benefit (expense)	(44,426)	(39,596)
Total reclassifications, net of tax	175,013	150,021
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	4,861,382
Other comprehensive income before reclassifications	(267,114)
Less: Amounts reclassified from AOCI	3,431
Balance, end of period	4,610,355	4,732,293
Reclassification from Accumulated Other Comprehensive Income
Amounts Reclassified From Accumulated Other Comprehensive Income [Abstract]
Total reclassifications before tax	4,343	2,835
Income tax benefit (expense)	(912)	(595)
Total reclassifications, net of tax	3,431	2,240
Accumulated other comprehensive income (loss)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other comprehensive income (loss), net of tax	(270,545)	(93,256)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	119,697	216,821
Balance, end of period	(150,848)	123,565
Net unrealized gains and (losses) on available-for-sale securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total other comprehensive income (loss)	(342,960)	(119,150)
Income tax benefit (expense)	72,022	25,021
Other comprehensive income (loss), net of tax	(270,938)	(94,129)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	150,038
Other comprehensive income before reclassifications	(267,114)
Less: Amounts reclassified from AOCI	3,824
Balance, end of period	(120,900)
Net unrealized gains and (losses) on available-for-sale securities | Reclassification from Accumulated Other Comprehensive Income
Amounts Reclassified From Accumulated Other Comprehensive Income [Abstract]
Total reclassifications before tax	4,841	3,940
Income tax benefit (expense)	(1,017)	(827)
Total reclassifications, net of tax	3,824	3,113
Net benefit plan assets and (obligations) recognized in shareholders' equity
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total other comprehensive income (loss)	498	1,105
Income tax benefit (expense)	(105)	(232)
Other comprehensive income (loss), net of tax	393	873
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(30,341)
Other comprehensive income before reclassifications	0
Less: Amounts reclassified from AOCI	(393)
Balance, end of period	(29,948)
Net benefit plan assets and (obligations) recognized in shareholders' equity | Reclassification from Accumulated Other Comprehensive Income
Amounts Reclassified From Accumulated Other Comprehensive Income [Abstract]
Total reclassifications before tax	(498)	(1,105)
Income tax benefit (expense)	105	232
Total reclassifications, net of tax	$ (393)	$ (873)