Stockholders' Equity and EPS - Reclassification out of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Gains on investment securities, net	$ 189,837	$ 29,849	$ 270,760	$ 106,575
Related tax benefit	(162,265)	(105,075)	(299,491)	(331,624)
Net interest income (loss)	527,740	520,644	1,564,804	1,562,933
Total reclassification adjustment for (gains) losses included in net income, net of tax	441,713	267,281	802,901	874,000
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassification adjustment for (gains) losses included in net income, net of tax	(11,568)	1,958	(68,733)	5,145
Accumulated Net Investment Gain (Loss) Attributable to Parent | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Gains on investment securities, net	0	0	(61,165)	3,905
Related tax benefit	0	0	16,953	(1,087)
Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Related tax benefit	(4,436)	755	9,403	(897)
Net interest income (loss)	$ (16,004)	$ 2,713	$ (33,924)	$ 3,224