Comprehensive Income - Reclassifications out of AOCI (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment securities gains, net		$ 19,139	$ 8,958
Interest on debt securities held to maturity		41,102	29,495
Interest and fees on loans		715,476	800,488
Interest on FHLB and other borrowings		(21,176)	(37,626)
Net (loss) income before income tax expense		(2,242,354)	176,584
Income tax (expense) benefit		5,069	(35,603)
Net (loss) income		(2,237,285)	140,981
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Unrealized Gains (Losses) on Debt Securities Available for Sale and Transferred to Held to Maturity
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment securities gains, net	[1]	19,139	8,958
Interest on debt securities held to maturity	[1]	(2,069)	(2,284)
Net (loss) income before income tax expense	[1]	17,070	6,674
Income tax (expense) benefit	[1]	(4,073)	(1,583)
Net (loss) income	[1]	12,997	5,091
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Accumulated Gains (Losses) on Cash Flow Hedging Instruments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest and fees on loans	[1]	5,459	(1,210)
Interest on FHLB and other borrowings	[1]	(419)	(169)
Net (loss) income before income tax expense	[1]	5,040	(1,379)
Income tax (expense) benefit	[1]	(1,202)	327
Net (loss) income	[1]	3,838	(1,052)
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Defined Benefit Plan Adjustment
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net periodic expense	[1],[2]	(2,301)	(4,089)
Income tax (expense) benefit	[1]	547	970
Net (loss) income	[1]	(1,754)	(3,119)
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Unamortized Impairment Losses on Debt Securities Held to Maturity
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest on debt securities held to maturity	[1]	(155)	(482)
Income tax (expense) benefit	[1]	37	114
Net (loss) income	[1]	$ (118)	$ (368)

[1] Amounts in parentheses indicate debits to the Unaudited Condensed Consolidated Statements of Income.

[2] These accumulated other comprehensive income components are included in the computation of net periodic pension cost (see Note 17, Benefit Plans, in the Notes to the December 31, 2019, Consolidated Financial Statements for additional details).