Non-consolidated VIEs - Corporation's VI in non-consolidated VIEs and max exposure to loss (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Variable Interest Entity
Assets	$ 66,870,268	$ 65,926,000	$ 52,803,639
Liabilities	60,972,709	59,897,313
Variable Interest Entity Not Primary Beneficiary
Variable Interest Entity
Total net assets	104,372	99,042
Maximum exposure to loss	104,372	99,042
Variable Interest Entity Not Primary Beneficiary | Servicing assets
Variable Interest Entity
Assets	94,890	90,273
Variable Interest Entity Not Primary Beneficiary | Mortgage servicing rights
Variable Interest Entity
Assets	94,890	90,273
Variable Interest Entity Not Primary Beneficiary | Other assets
Variable Interest Entity
Assets	9,482	8,769
Variable Interest Entity Not Primary Beneficiary | Servicing advances
Variable Interest Entity
Assets	$ 9,482	$ 8,769