Other comprehensive income (loss) - Reclassification out of accumulated other comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Reclassification out of accumulated other comprehensive loss
Income tax (benefit) expense	$ (83,542)	$ (41,168)	$ (233,466)	$ (68,893)
Net income	248,114	168,416	728,825	330,346
Reclassification out of accumulated other comprehensive income
Reclassification out of accumulated other comprehensive loss
Net income	(4,282)	(4,430)	(11,096)	(13,424)
Reclassification out of accumulated other comprehensive income | Adjustment of pension and postretirement benefit plan
Reclassification out of accumulated other comprehensive loss
Income (loss) before tax	(5,187)	(5,362)	(15,566)	(16,086)
Income tax (benefit) expense	1,945	2,011	5,840	6,033
Net income	(3,242)	(3,351)	(9,726)	(10,053)
Reclassification out of accumulated other comprehensive income | Amortization of net Loss
Reclassification out of accumulated other comprehensive loss
Other operating expenses	(5,187)	(5,362)	(15,566)	(16,086)
Reclassification out of accumulated other comprehensive income | Realized loss on sale of debt securities
Reclassification out of accumulated other comprehensive loss
Net gain (loss) on sale of debt securities	23	41	23	41
Income (loss) before tax	23	41	23	41
Income tax (benefit) expense	(5)	(6)	(5)	(6)
Net income	18	35	18	35
Reclassification out of accumulated other comprehensive income | Unrealized net (losses) gains on cash flow hedges
Reclassification out of accumulated other comprehensive loss
Income (loss) before tax	(1,518)	(1,613)	(1,707)	(5,127)
Income tax (benefit) expense	460	499	319	1,721
Net income	(1,058)	(1,114)	(1,388)	(3,406)
Reclassification out of accumulated other comprehensive income | Unrealized net (losses) gains on cash flow hedges | Forward contracts | Mortgage banking activities
Reclassification out of accumulated other comprehensive loss
Income (loss) before tax	(1,229)	(1,331)	(854)	(4,590)
Reclassification out of accumulated other comprehensive income | Unrealized net (losses) gains on cash flow hedges | Interest rate swap
Reclassification out of accumulated other comprehensive loss
Other Operating Income	$ (289)	$ (282)	$ (853)	$ (537)