Servicing rights - Residential mortgage servicing rights (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Servicing rights
Unpaid Principal Amount	$ 5,089,157	$ 2,145,133
Residential MSRs
Servicing rights
Unpaid Principal Amount	10,995,685	9,528,886
Fair Value	120,142	76,840	$ 91,174
Possible impact of adverse changes to key assumptions
Prepayment rate (10% adverse change)	(5,262)	(5,049)
Prepayment rate (20% adverse change)	(9,262)	(9,701)
Discount rate (10% adverse change)	(4,533)	(2,601)
Discount rate (20% adverse change)	(8,745)	(5,028)
Cost of servicing (10% adverse change)	(2,125)	(1,469)
Cost of servicing (20% adverse change)	(4,251)	(2,938)
Fannie Mae | Residential MSRs
Servicing rights
Unpaid Principal Amount	4,056,595	3,700,450
Fair Value	41,698	27,632
Ginnie Mae | Residential MSRs
Servicing rights
Unpaid Principal Amount	4,131,904	2,757,124
Fair Value	45,017	25,899
Freddie Mac
Servicing rights
Unpaid Principal Amount	4,232,969	1,501,998
Possible impact of adverse changes to key assumptions
Prepayment rate (10% adverse change)	(291)	(163)
Prepayment rate (20% adverse change)	(575)	(324)
Discount rate (10% adverse change)	(1,910)	(678)
Discount rate (20% adverse change)	(3,726)	(1,324)
Cost of servicing (10% adverse change)	(2,659)	(1,947)
Cost of servicing (20% adverse change)	(5,318)	(3,894)
Freddie Mac | Residential MSRs
Servicing rights
Unpaid Principal Amount	2,807,186	3,071,312
Fair Value	$ 33,427	$ 23,309
Minimum | Residential MSRs
Servicing rights, valuation assumptions
Forward prepayment assumptions	8.40%	12.60%
Discount rate	9.00%	9.10%
Cost of servicing	$ 70	$ 70
Minimum | Freddie Mac
Servicing rights, valuation assumptions
Forward prepayment assumptions	0.00%	0.10%
Discount rate	6.00%	6.00%
Servicing expense (as a percent)	0.00%	0.20%
Maximum | Residential MSRs
Servicing rights, valuation assumptions
Forward prepayment assumptions	20.90%	31.40%
Discount rate	11.00%	11.70%
Cost of servicing	$ 85	$ 85
Maximum | Freddie Mac
Servicing rights, valuation assumptions
Forward prepayment assumptions	7.30%	5.10%
Discount rate	6.00%	6.00%
Servicing expense (as a percent)	0.80%	0.30%
Weighted Average | Residential MSRs
Servicing rights, valuation assumptions
Forward prepayment assumptions	9.50%	14.30%
Discount rate	9.40%	9.80%
Cost of servicing	$ 74	$ 74
Weighted Average | Freddie Mac
Servicing rights, valuation assumptions
Forward prepayment assumptions	3.50%	2.40%
Discount rate	6.00%	6.00%
Servicing expense (as a percent)	0.10%	0.20%